drm/xe: Define CACHE_MODE_1 as MCR register

drm/xe: Define CACHE_MODE_1 as MCR register

CACHE_MODE_1 is a MCR register for all platforms that currently use it
in the Xe driver.  Use XE_REG_MCR() when defining it.

Fixes: 8cd7e9759766 ("drm/xe: Add missing DG2 lrc workarounds")
Fixes: ff063430caa8 ("drm/xe/mtl: Add some initial MTL workarounds")
Bspec: 66534, 67788
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patch.msgid.link/20260514-rtp-mcr-check-v3-1-30dd47855fee@intel.com
Signed-off-by: Gustavo Sousa <gustavo.sousa@intel.com>