drm/i915/display: update handling of FBC when VT-d active workaround

drm/i915/display: update handling of FBC when VT-d active workaround

Move the handling of the disabling FBC when VT-d is active wa
as part of the intel_fbc_check_plane(). As the hw is still there,
intel_fbc_sanitize should be able to handle the state properly.

v2: update the patch description (Jani Nikula)

v3: fix the return value in wa handling (Jani Nikula)

Bspec: 21664
Suggested-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Vinod Govindapillai <vinod.govindapillai@intel.com>
Reviewed-by: Jouni Högander <jouni.hogander@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240528114826.134958-1-vinod.govindapillai@intel.com