arm64: dts: rockchip: remove px30 emmc_pwren pinctrl

That gpio1-b0 can only be flash_cs apart from a regular gpio,
so there is no power-related pinmux for the emmc for this pin.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://lore.kernel.org/r/20190917082659.25549-3-heiko@sntech.de