Describe the SD1_VSELECT pad, which is necessary to allow UHS modes.

Also, to support higher SD card speed modes, describe the 100MHz and
200MHz SD card pinctrl entries.
Suggested-by: Ye Li <ye.li@nxp.com>
Signed-off-by: Fabio Estevam <festevam@denx.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>