drm/xe/xe2: Add Wa_15015404425

Wa_15015404425 asks us to perform four "dummy" writes to a
non-existent register offset before every real register read.
Although the specific offset of the writes doesn't directly
matter, the workaround suggests offset 0x130030 as a good target
so that these writes will be easy to recognize and filter out in
debugging traces.

V5(MattR):
  - Avoid negating an equality comparison
V4(MattR):
  - Use writel and remove xe_reg usage
V3(MattR):
  - Define dummy reg local to function
  - Avoid tracing dummy writes
  - Update commit message
V2:
  - Add WA to 8/16/32bit reads also - MattR
  - Corrected dummy reg address - MattR
  - Use for loop to avoid mental pause - JaniN

Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Tejas Upadhyay <tejas.upadhyay@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240709155606.2998941-1-tejas.upadhyay@intel.com