drm/xe/uapi: Use LR abbrev for long-running vms

drm/xe/uapi: Use LR abbrev for long-running vms

Currently we're using "compute mode" for long running VMs using
preempt-fences for memory management, and "fault mode" for long
running VMs using page faults.

Change this to use the terminology "long-running" abbreviated as LR for
long-running VMs. These VMs can then either be in preempt-fence mode or
fault mode. The user can force fault mode at creation time, but otherwise
the driver can choose to use fault- or preempt-fence mode for long-running
vms depending on the device capabilities. Initially unless fault-mode is
specified, the driver uses preempt-fence mode.

v2:
- Fix commit message wording and the documentation around
  CREATE_FLAG_LR_MODE and CREATE_FLAG_FAULT_MODE

Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Francois Dugast <francois.dugast@intel.com>
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Signed-off-by: Francois Dugast <francois.dugast@intel.com>
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>