boards: imx93_evk: enable SDHC on the board

Added pinctrl and dts nodes for uSDHC1 and uSDHC2, they are disabled
by default, and provided overlay files to enable them if needed.

Signed-off-by: Jiafei Pan <Jiafei.Pan@nxp.com>
Signed-off-by: Lei Xu <lei.xu@nxp.com>