arm64: dts: rockchip: add GRF GPIO controller to rk3328

Adding a GRF GPIO controller labled "grf_gpio" to rk3328, currently
providing access to the GPIO_MUTE pin, which is manupulated by the
GRF_SOC_CON10 register.

The GPIO_MUTE pin is referred to as <&grf_gpio 0>.

Signed-off-by: Levin Du <djw@t-chip.com.cn>
[dropped default-status disabled]
Signed-off-by: Heiko Stuebner <heiko@sntech.de>