dt-bindings: modify document of Rockchip power domains

Rockchip Socs contain quality of service (qos) blocks managing priority,
bandwidth, etc of the connection of each domain to the interconnect.
These blocks loose state when their domain gets disabled and therefore
need to be saved when disabling and restored when enabling a power-domain.

These qos blocks also are similar over all currently available Rockchip
SoCs.

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