drm/xe: Restore engine registers before restarting schedulers after GT reset

drm/xe: Restore engine registers before restarting schedulers after GT reset

During GT reset recovery in do_gt_restart(), xe_uc_start() was called
before xe_reg_sr_apply_mmio() restored engine-specific registers. This
created a race window where the scheduler could run jobs before hardware
state was fully restored.

This caused failures in eudebug tests (xe_exec_sip_eudebug@breakpoint-
waitsip-*) where TD_CTL register (containing TD_CTL_GLOBAL_DEBUG_ENABLE)
wasn't restored before jobs started executing. Breakpoints would fail to
trigger SIP entry because the debug enable bit wasn't set yet.

Fix by moving xe_uc_start() after all MMIO register restoration,
including engine registers and CCS mode configuration, ensuring all
hardware state is fully restored before any jobs can be scheduled.

Fixes: dd08ebf6c352 ("drm/xe: Introduce a new DRM driver for Intel GPUs")
Signed-off-by: Jan Maslak <jan.maslak@intel.com>
Reviewed-by: Jonathan Cavitt <jonathan.cavitt@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patch.msgid.link/20251210145618.169625-2-jan.maslak@intel.com