drm/xe/configfs: Add attribute to disable engines

Add the userspace interface to load the driver with fewer engines.
The syntax is to just echo the engine names to a file in configfs, like
below:

	echo 'rcs0,bcs0' > /sys/kernel/config/xe/<bdf>/engine_allowed

With that engines other than rcs0 and bcs0 will not be enabled. To
enable all instances from a class, a '*' can be used.

Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://lore.kernel.org/r/20250528-engine-mask-v4-4-f4636d2a890a@intel.com


Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>