drm/xe/pxp/uapi: Add a query for PXP status

PXP prerequisites (SW proxy and HuC auth via GSC) are completed
asynchronously from driver load, which means that userspace can start
submitting before we're ready to start a PXP session. Therefore, we need
a query that userspace can use to check not only if PXP is supported but
also to wait until the prerequisites are done.

v2: Improve doc, do not report TYPE_NONE as supported (José)
v3: Better comments, remove unneeded copy_from_user (John)

Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: José Roberto de Souza <jose.souza@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/20250129174140.948829-10-daniele.ceraolospurio@intel.com