drm/xe: Clean up xe_device_desc

drm/xe: Clean up xe_device_desc

Now that most of the characteristics of a device are associated with the
graphics and media IPs, the remaining contents of xe_device_desc can be
cleaned up a bit:

 * 'gt' is unused; drop it
 * DEV_INFO_FOR_EACH_FLAG only covers two flags and is only used in this
   one file; drop the unnecessary macro complexity
 * Convert .has_4tile to a single bitfield bit so that it can be packed
   with the other feature flags
 * Move 'platform' lower in the structure for better packing

Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://lore.kernel.org/r/20230406235621.1914492-10-matthew.d.roper@intel.com
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>