drm/xe: Add max engine priority to xe query

Intel Vulkan driver needs to know what is the maximum priority to fill
a device info struct for applications.

Right now we getting this information by creating a engine and setting
priorities from min to high to know what is the maximum priority for
running process but this leads to info messages to be printed to
dmesg:

xe 0000:03:00.0: [drm] Ioctl argument check failed at drivers/gpu/drm/xe/xe_engine.c:178: value == DRM_SCHED_PRIORITY_HIGH && !capable(CAP_SYS_NICE)

It does not cause any harm but when executing a test suite like
crucible it causes thousands of those messages to be printed.

So here adding one more property to drm_xe_query_config to fetch the
max engine priority.

Cc: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>