drm/i915/dsb: Align DSB register writes to 8 bytes

Every DSB instruction has to be 8byte aligned. Make sure
that is the case for the non-indexed register writes as well.
The way this could end up unaligned is we emitted an odd
number of indexed register writes beforehand.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221216003810.13338-4-ville.syrjala@linux.intel.com


Reviewed-by: Animesh Manna <animesh.manna@intel.com>