drm/xe/pat: Add helper to query compression enable status

drm/xe/pat: Add helper to query compression enable status

Add xe_pat_index_get_comp_en() helper function to check whether
compression is enabled for a given PAT index by extracting the
XE2_COMP_EN bit from the PAT table entry.

There are no current users, however there are multiple in-flight series
which will all use this helper.

CC: Nitin Gote <nitin.r.gote@intel.com>
CC: Sanjay Yadav <sanjay.kumar.yadav@intel.com>
CC: Matt Roper <matthew.d.roper@intel.com>
Suggested-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Xin Wang <x.wang@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Nitin Gote <nitin.r.gote@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Sanjay Yadav <sanjay.kumar.yadav@intel.com>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patch.msgid.link/20251110221458.1864507-2-x.wang@intel.com