drm/lima: add pm resume/suspend ops

Add driver pm system and runtime hardware resume/suspend ops.
Note this won't enable runtime pm of the device yet.

v2:
Do clock and power gating when suspend/resume.

Tested-by: Bhushan Shah <bshah@kde.org>
Reviewed-by: Vasily Khoruzhick <anarsoul@gmail.com>
Signed-off-by: Qiang Yu <yuq825@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200421133551.31481-10-yuq825@gmail.com