dt-bindings: rockchip-dw-mshc: add RK3036 dw-mshc description

rk3036 dtsi file add dw-mshc compatible "rockchip,rk3036-dw-mshc"
but didn't add it into rockchip-dw-mshc.txt.

Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>