drm/xe: Introduce GuC PC debugfs

Allows the visualization of the current GuC power conservation
status and policies.

v2: Fix DCC msg (Vinay)
v3: Simplify pc_get_state_string (Jonathan)

Reviewed-by: Vinay Belgaumkar <vinay.belgaumkar@intel.com>
Reviewed-by: Jonathan Cavitt <jonathan.cavitt@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250115145053.1142023-1-rodrigo.vivi@intel.com


Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>