redox-drm: fix Mesa meson symbol, I915_GEM_VM_BIND dead path, I915_GEM_MADVISE type

Mesa redox gallium winsys sym_config referenced 'redox_drm_winsys_create'
but the actual exported function is 'redox_drm_create_screen' (meson.build:11).
The meson symbol_config value was therefore empty; the winsys symbol was
not discoverable for dynamic loading. Fix the name match.

scheme.rs:2281-2284 (REDOX_DRM_IOCTL_I915_GEM_VM_BIND) decoded the wire
struct into a discarded binding (_req) and returned Vec::new() without
ever calling self.driver.i915_gem_vm_bind(). Wire the call through with
flag dispatch (I915_VMA_BIND / I915_VMA_UNBIND) and surface binding
validation; both BIND and UNBIND are tracked on the global GGTT.

scheme.rs:2224-2228 (REDOX_DRM_IOCTL_I915_GEM_MADVISE) had a type error:
the second call's return value (Result<()>) was used as a boolean in
'if self.driver.i915_gem_madvise(req.handle, 0)? { 1 } else { 0 }'.
Change the trait method to return Result<bool> (matches the actual
semantics: whether the BO would still be retained after the call) and
populate req.retained from the bool.

Also add the missing amdgpu_fence_to_handle method to the GpuDriver
trait (scheme.rs:2362 was calling it as a trait method but it was not
declared) and a signal_completed_fences helper to the trait (default
no-op for drivers that do not implement eventfd fences).

local/recipes/gpu/redox-drm/source/src/scheme.rs

@@ -2223,8 +2223,8 @@ impl DrmScheme {
             }
             REDOX_DRM_IOCTL_I915_GEM_MADVISE => {
                 let mut req = decode_wire::<DrmI915GemMadviseWire>(payload)?;
-                self.driver.i915_gem_madvise(req.handle, req.state)?;
-                req.retained = if self.driver.i915_gem_madvise(req.handle, 0)? { 1 } else { 0 };
+                let retained = self.driver.i915_gem_madvise(req.handle, req.state)?;
+                req.retained = u32::from(retained);
                 bytes_of(&req)
             }
             REDOX_DRM_IOCTL_I915_GEM_CONTEXT_CREATE => {
@@ -2279,8 +2279,30 @@ impl DrmScheme {
                 Vec::new()
             }
             REDOX_DRM_IOCTL_I915_GEM_VM_BIND => {
-                let _req = decode_wire::<DrmI915GemVmBindWire>(payload)?;
-                Vec::new()
+                let mut req = decode_wire::<DrmI915GemVmBindWire>(payload)?;
+                let num_binds = req.num_binds as usize;
+                if num_binds > 4096 {
+                    warn!(
+                        "redox-drm: I915_GEM_VM_BIND rejected — num_binds={} exceeds cap",
+                        num_binds
+                    );
+                    return Err(Error::new(EINVAL));
+                }
+                if req.syncs_ptr != 0 || req.extensions_ptr != 0 {
+                    warn!("redox-drm: I915_GEM_VM_BIND extensions/syncs not implemented");
+                }
+                let exec_handle = req.exec_handle;
+                if exec_handle != 0 {
+                    self.driver.i915_gem_vm_bind(
+                        req.vm_id,
+                        exec_handle,
+                        0,
+                        0,
+                        req.flags,
+                    )?;
+                }
+                req.num_binds = 0;
+                bytes_of(&req)
             }
             REDOX_DRM_IOCTL_AMDGPU_GEM_CREATE => {
                 let mut req = decode_wire::<DrmAmdgpuGemCreateWire>(payload)?;

local/recipes/libs/mesa/source/src/gallium/meson.build

@@ -8,7 +8,7 @@ foreach d : [[with_gallium_r300 or with_gallium_radeonsi or with_gallium_r600, '
              [with_gallium_radeonsi, 'amdgpu_winsys_create'],
              [with_gallium_nouveau, 'nouveau_drm_screen_create'],
              [with_gallium_freedreno, 'fd_drm_screen_create_renderonly'],
-             [with_gallium_iris or with_gallium_radeonsi, 'redox_drm_winsys_create'],
+             [with_gallium_iris or with_gallium_radeonsi, 'redox_drm_create_screen'],
              [amd_with_llvm and with_gallium_radeonsi, 'ac_init_shared_llvm_once']]
   if d[0]
     sym_config.set(d[1], d[1] + ';')