drm/i915: Track logically enabled planes for hw state

Currently crtc_state->uapi.plane_mask only tracks logically
enabled planes on the uapi level. For bigjoiner purposes
we want to do the same for the hw state. Let's follow the
pattern established by active_planes & co. here.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201124201156.17095-1-ville.syrjala@linux.intel.com


Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>