drm/i915/fbc: Relocate intel_fbc_override_cfb_stride()

Move intel_fbc_override_cfb_stride() next to its cousins.
Helps with later patches.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211124113652.22090-5-ville.syrjala@linux.intel.com


Reviewed-by: Mika Kahola <mika.kahola@intel.com>