drm/arm/malidp: Added the late system pm functions

drm/arm/malidp: Added the late system pm functions

malidp_pm_suspend_late checks if the runtime status is not suspended
and if so, invokes malidp_runtime_pm_suspend which disables the
display engine/core interrupts and the clocks. It sets the runtime status
as suspended.

The difference between suspend() and suspend_late() is as follows:-
1. suspend() makes the device quiescent. In our case, we invoke the DRM
helper which disables the CRTC. This would have invoked runtime pm
suspend but the system suspend process disables runtime pm.
2. suspend_late() It continues the suspend operations of the drm device
which was started by suspend(). In our case, it performs the same functionality
as runtime_suspend().

The complimentary functions are resume() and resume_early(). In the case of
resume_early(), we invoke malidp_runtime_pm_resume() which enables the clocks
and the interrupts. It sets the runtime status as active. If the device was
in runtime suspend mode before system suspend was called, pm_runtime_work()
will put the device back in runtime suspended mode( after the complete system
has been resumed).

Signed-off-by: Ayan Kumar Halder <ayan.halder@arm.com>
Acked-by: Liviu Dudau <liviu.dudau@arm.com>
Signed-off-by: Liviu Dudau <liviu.dudau@arm.com>