drm/rockchip: add an common abstracted PSR driver

The PSR driver have exported four symbols for specific device driver, and
it's safe to call them in interrupt context:
- rockchip_drm_psr_register()
- rockchip_drm_psr_unregister()
- rockchip_drm_psr_enable()
- rockchip_drm_psr_disable()
- rockchip_drm_psr_flush()

Encoder driver should call the register/unregister interfaces to hook
itself into common PSR driver, encoder have implement the 'psr_set'
callback which use the set PSR state in hardware side.

Crtc driver would call the enable/disable interfaces when vblank is
enable/disable, after that the common PSR driver would call the encoder
registered callback to set the PSR state.

Fb driver would call the flush interface in 'fb->dirty' callback, this
helper function would force all PSR enabled encoders to exit from PSR
for 3 seconds.

Signed-off-by: Yakir Yang <ykk@rock-chips.com>
[seanpaul removed leftover psr_enabled/psr_work kruft from drm_vop.c]
Signed-off-by: Sean Paul <seanpaul@chromium.org>