drm/i915/icl: Handle expanded PLANE_CTL_FORMAT field

ICL+ adds changes the PLANE_CTL_FORMAT field from [27:24] to [27:23],
however, all existing PLANE_CTL_FORMAT_* definitions still map to the
correct values.  Add an ICL_PLANE_CTL_FORMAT_MASK definition, and use
that for masking for the conversion to fourcc.

v2: No changes

v3: Change new definition name, drop comment (Rodrigo)

Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: James Ausmus <james.ausmus@intel.com>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180130134918.32283-8-paulo.r.zanoni@intel.com