drm/meson: add resume/suspend hooks

Add the suspend and resume hooks to:
- save and disable the entire DRM driver on suspend
- re-init the entire VPU subsystem on resume, to recover CRTC and pixel
generator functionnal usage after DDR suspend, then recover DRM driver
state

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Tested-by: Kevin Hilman <khilman@baylibre.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190827095825.21015-3-narmstrong@baylibre.com