drm/i915/fbc: Split plane rotation checks per-platform

drm/i915/fbc: Split plane rotation checks per-platform

Carve up rotation_is_valid() into per-platform variants to
make it easier to see what limits are actually being imposed.

TODO: maybe go for vfuncs later

Reviewed-by: Juha-Pekka Heikkila <juhapekka.heikkila@gmail.com>
Reviewed-by: Vinod Govindapillai <vinod.govindapillai@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231003194256.28569-4-ville.syrjala@linux.intel.com