drm/xe/pat: Default XE_CACHE_NONE_COMPRESSION to invalid

drm/xe/pat: Default XE_CACHE_NONE_COMPRESSION to invalid

Initialize XE_CACHE_NONE_COMPRESSION PAT index to XE_PAT_INVALID_IDX by
default, same as XE_CACHE_WB_COMPRESSION. Platforms that support this
cache mode will override it in xe_pat_init_early(). This ensures that
accidental use on unsupported platforms can be detected.

A subsequent patch introduces a helper to assert on invalid PAT index
access at all call sites.

Suggested-by: Matthew Auld <matthew.auld@intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Xin Wang <x.wang@intel.com>
Link: https://patch.msgid.link/20260416045526.536497-3-x.wang@intel.com
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>