xilinx: Fix xlnx,mio_bank property

s/xlnx,mio_bank/xlnx,mio-bank/g

DT binding is describing mio-bank not mio_bank that's why fix all DTSes and
also driver itself.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Acked-by: Peng Fan <peng.fan@nxp.com>