drm/vc4: Use drm_crtc_mask()

Use drm_crtc_mask() where appropriate.

Cc: Eric Anholt <eric@anholt.net>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180626194716.12522-9-ville.syrjala@linux.intel.com


Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Eric Anholt <eric@anholt.net>