dt-bindings: add used but undocumented rockchip grf compatible values

There are some more General Register Files used in devicetree files
already, but as of now undocumented in the binding document, fix that.
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Shawn Lin <shawn.lin@rock-chips.com>

Documentation/devicetree/bindings/soc/rockchip/grf.txt

@@ -5,11 +5,13 @@ is composed of many registers for system control.
 
 From RK3368 SoCs, the GRF is divided into two sections,
 - GRF, used for general non-secure system,
+- SGRF, used for general secure system,
 - PMUGRF, used for always on system
 
 Required Properties:
 
 - compatible: GRF should be one of the followings
+   - "rockchip,rk3036-grf", "syscon": for rk3036
    - "rockchip,rk3066-grf", "syscon": for rk3066
    - "rockchip,rk3188-grf", "syscon": for rk3188
    - "rockchip,rk3228-grf", "syscon": for rk3228
@@ -19,6 +21,8 @@ Required Properties:
 - compatible: PMUGRF should be one of the followings
    - "rockchip,rk3368-pmugrf", "syscon": for rk3368
    - "rockchip,rk3399-pmugrf", "syscon": for rk3399
+- compatible: SGRF should be one of the following
+   - "rockchip,rk3288-sgrf", "syscon": for rk3288
 - reg: physical base address of the controller and length of memory mapped
   region.