arm64: zynqmp: Add pinctrl emmc description to SM-K26

Production SOM has emmc on it and make sense to describe pin description to
be able use EMMC if it is not configured via psu_init.
(Still some regs are not handled but this is one step in that direction)

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Link: https://lore.kernel.org/r/3545a0f08d342de98efc82b78f5725eda091555a.1647267969.git.michal.simek@xilinx.com