drm/i915/gem: Use large rings for compute contexts

Allow compute contexts to submit the maximal amount of work without
blocking userspace.

The original size for user LRC ring's (SZ_16K) was chosen to minimise
memory consumption, without being so small as to frequently stall in the
middle of workloads. With the main consumers being GL / media pipelines
of 2 or 3 batches per frame, we want to support ~10 requests in flight
to allow for the application to control throttling without stalling
within a frame.

v2:
  - cover with else part

Signed-off-by: Chris Wilson <chris.p.wilson@intel.com>
Signed-off-by: Tejas Upadhyay <tejas.upadhyay@intel.com>
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Signed-off-by: Andi Shyti <andi.shyti@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230517135754.1110291-1-tejas.upadhyay@intel.com