soc: rockchip: power-domain: Support domain control in hiword-registers

New Rockchips SoCs may have their power-domain control in registers
using a writemask-based access scheme (upper 16bit being the write
mask). So add a DOMAIN_M type and handle this case accordingly.

Signed-off-by: Elaine Zhang <zhangqing@rock-chips.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>