Add a function for emitting masked register writes.

Note that the mask is implemented through byte enables,
so can only mask off aligned 8bit sets of bits.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230606191504.18099-10-ville.syrjala@linux.intel.comReviewed-by: Uma Shankar <uma.shankar@intel.com>