UPSTREAM: drm/i915/dsb: Nuke the MMIO->indexed register write logic

We've determined that indexed DSB writes are only faster
than MMIO writes when writing the same register ~5 or more
times. That seems very unlikely to happen in any other case
than when using indexed LUT registers. Simplify the code
by removing the MMIO->indexed write conversion logic and
just emit the instruction as an indexed write from the get go.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241120164123.12706-4-ville.syrjala@linux.intel.com


Reviewed-by: Uma Shankar <uma.shankar@intel.com>
(cherry picked from commit da5bb897)

Bug: 432032023
Test: None
Change-Id: Id9e68c5a53fc6856170338c1e5bb8f82b36d81da
Signed-off-by: Ap, Kamal <kamal.ap@intel.corp-partner.google.com>