drm/xe/pxp: Allocate PXP execution resources

PXP requires submissions to the HW for the following operations

1) Key invalidation, done via the VCS engine
2) Communication with the GSC FW for session management, done via the
   GSCCS.

Key invalidation submissions are serialized (only 1 termination can be
serviced at a given time) and done via GGTT, so we can allocate a simple
BO and a kernel queue for it.

Submissions for session management are tied to a PXP client (identified
by a unique host_session_id); from the GSC POV this is a user-accessible
construct, so all related submission must be done via PPGTT. The driver
does not currently support PPGTT submission from within the kernel, so
to add this support, the following changes have been included:

- a new type of kernel-owned VM (marked as GSC), required to ensure we
  don't use fault mode on the engine and to mark the different lock
  usage with lockdep.
- a new function to map a BO into a VM from within the kernel.

v2: improve comments and function name, remove unneeded include (John)
v3: fix variable/function names in documentation

Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.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/20250129174140.948829-3-daniele.ceraolospurio@intel.com