drm/xe/pxp: Add PXP debugfs support

This patch introduces 2 PXP debugfs entries:

- info: prints the current PXP status and key instance
- terminate: simulate a termination interrupt

The first one is useful for debug, while the second one can be used for
testing the termination flow.

v2: move the info prints inside the lock (John)

Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: John Harrison <John.C.Harrison@Intel.com>
Reviewed-by: John Harrison <John.C.Harrison@Intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250129174140.948829-13-daniele.ceraolospurio@intel.com