drm/i915/xehp: Define context scheduling attributes in lrc descriptor

In Dual Context mode the EUs are shared between render and compute
command streamers. The hardware provides a field in the lrc descriptor
to indicate the prioritization of the thread dispatch associated to the
corresponding context.

The context priority is set to 'low' at creation time and relies on the
existing context priority to set it to low/normal/high.

Bspec: 46145, 46260
Original-author: Michel Thierry
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Signed-off-by: Aravind Iddamsetty <aravind.iddamsetty@intel.com>
Signed-off-by: Prasad Nallani <prasad.nallani@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220301231549.1817978-8-matthew.d.roper@intel.com