drm/rockchip: vop2: fix suspend/resume

During a suspend/resume cycle the VO power domain will be disabled and
the VOP2 registers will reset to their default values. After that the
cached register values will be out of sync and the read/modify/write
operations we do on the window registers will result in bogus values
written. Fix this by re-initializing the register cache each time we
enable the VOP2. With this the VOP2 will show a picture after a
suspend/resume cycle whereas without this the screen stays dark.

Fixes: 604be855

 ("drm/rockchip: Add VOP2 driver")
Cc: stable@vger.kernel.org
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Tested-by: Chris Morgan <macromorgan@hotmail.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20230413144347.3506023-1-s.hauer@pengutronix.de