rockchip: rk3188: Add sysreset driver

Driver for the sysreset of Rockchip rk3188 socs.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
Tested-by: Kever Yang <kever.yang@rock-chips.com>