drm/xe/pxp: Add PXP queue tracking and session start

We expect every queue that uses PXP to be marked as doing so, to allow
the driver to correctly manage the encryption status. The API for doing
this from userspace is coming in the next patch, while this patch
implement the management side of things. When a PXP queue is created,
the driver will do the following:

- Start the default PXP session if it is not already running;
- assign an rpm ref to the queue to keep for its lifetime (this is
  required because PXP HWDRM sessions are killed by the HW suspend flow).

Since PXP start and termination can race each other, this patch also
introduces locking and a state machine to keep track of the pending
operations. Note that since we'll need to take the lock from the
suspend/resume paths as well, we can't do submissions while holding it,
which means we need a slightly more complicated state machine to keep
track of intermediate steps.

v4: new patch in the series, split from the following interface patch to
keep review manageable. Lock and status rework to not do submissions
under lock.

v5: Improve comments and error logs (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/20250129174140.948829-8-daniele.ceraolospurio@intel.com

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