drm/xe/pat: Add debugfs node to dump PAT

This is useful to debug cache issues, to double check if the PAT
indexes match what they were supposed to be set to from spec.

v2: Add separate functions for XeHP, XeHPC and XeLPG so it correctly
    reads the index based on MCR/REG registers and also decodes the
    fields (Matt Roper)
v3: Starting with XeHPC, do not translate values to human-readable
    formats as the main goal is to make it easy to compare the table
    with the spec. Also, share a single array for xelp/xehp str map
    (Matt Roper)

Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://lore.kernel.org/r/20231006182325.3617685-3-lucas.demarchi@intel.com


Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>