rockchip: rk3568-rock-3a: Use pinctrl for sdmmc and sdhci in SPL

Enable pinctrl for sdmmc and sdhci in SPL to support loading of FIT
image from SD and eMMC storage when booting from SPI NOR flash.

Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>