drm/i915/fbc: handle dirty rect coords for the first frame

drm/i915/fbc: handle dirty rect coords for the first frame

During enabling FBC, for the very first frame, the prepare dirty
rect routine wouldnt have executed as at that time the plane
reference in the fbc_state would be NULL. So this could make
driver program some invalid entries as the damage area. Though
fbc hw ignores the dirty rect values programmed for the first
frame after enabling FBC, driver must ensure that valid dirty
rect coords are programmed. So ensure that for the first frame
correct dirty rect coords are updated to the HW.

Signed-off-by: Vinod Govindapillai <vinod.govindapillai@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Mika Kahola <mika.kahola@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250228093802.27091-10-vinod.govindapillai@intel.com