drm/i915: Account ring buffer and context state storage

Account ring buffers and logical context space against the owning client
memory usage stats.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Aravind Iddamsetty <aravind.iddamsetty@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231107101806.608990-4-tvrtko.ursulin@linux.intel.com