drm/i915/dsb: Allow the caller to pass in the DSB buffer size

drm/i915/dsb: Allow the caller to pass in the DSB buffer size

The caller should more or less know how many DSB commands it
wants to emit into the command buffer, so allow it to specify
the size of the command buffer rather than having the low level
DSB code guess it.

Technically we can emit as many as 134+1033 (for adl+ degamma +
10bit gamma) register writes but thanks to the DSB indexed register
write command we get significant space savings so the current size
estimate of 8KiB (~1024 DSB commands) is sufficient for now.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221216003810.13338-11-ville.syrjala@linux.intel.com
Reviewed-by: Animesh Manna <animesh.manna@intel.com>