drm/lima: add usage counting method to ctx_mgr

lima maintains a context manager per drm_file, similar to amdgpu.
In order to account for the complete usage per drm_file, all of the
associated contexts need to be considered.
Previously released contexts also need to be accounted for but their
drm_sched_entity info is gone once they get released, so account for it
in the ctx_mgr.

Signed-off-by: Erico Nunes <nunes.erico@gmail.com>
Signed-off-by: Qiang Yu <yuq825@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230312233052.21095-2-nunes.erico@gmail.com