redox-drm: validate connector state in atomic_check (Gap 8 fix)

atomic_check previously ignored the _available_connectors parameter
(prevented by underscore prefix). The CRTC state's connectors: Vec<u32>
field declared which connectors to bind, but atomic_check never
verified they actually existed or were connected. This allowed
client commits to reference phantom or disconnected connectors
and silently produce invalid state.

Fix: use the available_connectors slice to validate that each
referenced connector ID exists in hardware and has connection
status Connected. Return CrtcNotFound or ConnectorDisconnected
respectively so the kernel rejects invalid commits with a clear
error rather than producing a malformed display state.

This unblocks libdrm drmModeAtomicCommit callers that rely on
DRM_MODE_ATOMIC_ALLOW_MODESET returning success only for valid
connector configurations.

local/recipes/gpu/redox-drm/source/src/kms/atomic.rs

@@ -1,6 +1,6 @@
 
 
-use super::{ConnectorInfo, ModeInfo};
+use super::{ConnectorInfo, ConnectorStatus, ModeInfo};
 
 /// Maximum pixel clock in kHz that the display engine supports.
 const MAX_PIXEL_CLOCK_KHZ: u32 = 600_000;
@@ -125,7 +125,7 @@ pub enum AtomicCheckResult {
 /// Validate the atomic state against hardware constraints.
 pub fn atomic_check(
     state: &AtomicState,
-    _available_connectors: &[ConnectorInfo],
+    available_connectors: &[ConnectorInfo],
 ) -> AtomicCheckResult {
     for crtc in &state.crtc_states {
         if !crtc.active {
@@ -175,6 +175,22 @@ pub fn atomic_check(
                 reason: "active CRTC has no framebuffer assigned".into(),
             };
         }
+
+        for conn_id in &crtc.connectors {
+            match available_connectors.iter().find(|c| c.id == *conn_id) {
+                None => {
+                    return AtomicCheckResult::CrtcNotFound {
+                        crtc_id: *conn_id,
+                    };
+                }
+                Some(conn) if conn.connection != ConnectorStatus::Connected => {
+                    return AtomicCheckResult::ConnectorDisconnected {
+                        connector_id: *conn_id,
+                    };
+                }
+                Some(_) => {}
+            }
+        }
     }
 
     AtomicCheckResult::Ok