intel: Phase 7+8 — debug/observability and GuC submission

- hangcheck.rs: GpuErrorState struct with full register snapshot
- guc.rs: CTB channels (H2G/G2H) with GGTT descriptors, ADS setup
- mod.rs: wire CTB init and ADS setup after GuC firmware upload

local/recipes/gpu/redox-drm/source/src/drivers/intel/guc.rs

@@ -244,7 +244,7 @@ impl GucFirmware {
     pub fn init_ctb_channels(&mut self, gtt: &mut IntelGtt) -> Result<()> {
         if !self.loaded {
             return Err(DriverError::Initialization(
-                "cannot init CTB before GuC firmware is loaded",
+                "cannot init CTB before GuC firmware is loaded".into(),
             ));
         }