arm64: dts: rockchip: fix nanopc-t6 sdmmc regulator

sdmmc on the nanopc-t6 is powered by vcc3v3_sd_s0, not vcc_3v3_s3
add the vcc3v3_sd_s0 regulator, and control it with gpio4_a5

Signed-off-by: John Clark <inindev@gmail.com>
Link: https://lore.kernel.org/r/20240102024054.1030313-1-inindev@gmail.com
Signed-off-by: Heiko Stuebner <heiko@sntech.de>