drm/i915/guc: Add CT size delay helper

As of now, there is no mechanism for tracking a given request's
progress through the queue.  Instead, add a helper that returns
an estimated maximum time the queue should take to drain if
completely full.

Suggested-by: John Harrison <john.c.harrison@intel.com>
Signed-off-by: Jonathan Cavitt <jonathan.cavitt@intel.com>
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Acked-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Nirmoy Das <nirmoy.das@intel.com>
Reviewed-by: John Harrison <john.c.harrison@intel.com>
Signed-off-by: Andi Shyti <andi.shyti@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231017180806.3054290-3-jonathan.cavitt@intel.com