drm/i915/fbc: Move stuff from intel_fbc_can_enable() into intel_fbc_check_plane()

Don't really see a good reason why we can't just do the vgpu and
modparam checks already in intel_fbc_check_plane().

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211124113652.22090-15-ville.syrjala@linux.intel.com


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