[ARM] OpenRD: Enable SD/UART selection for serial port 1

This patch enables users to choose either the SDIO interface or UART1
(RS232/RS485). The selection can be done through kernel parameter.

By default the port would be used for SDIO interface. Passing the string
"kw_openrd_init_uart1=232" or "kw_openrd_init_uart1=485" enables either
the RS-232 or RS-485 port respectively; disabling the SDIO interface.
Anything else selects the default SDIO interface.

"kw_openrd_init_uart1=485" is ignored on OpenRD-Base as it doesn't
have RS485 port.

Signed-off-by: Tanmay Upadhyay <tanmay.upadhyay@einfochips.com>
Acked-by: Alexander Clouter <alex@digriz.org.uk>
Signed-off-by: Nicolas Pitre <nico@fluxnic.net>