[ARM] 5276/1: ep93xx: allow selecting UART for early kernel messages

Currently on the EP93xx platform early kernel messages go to UART1.
Since this UART is the only one that has modem control signals it
might be used for another purpose and it is undesirable for those
messages to appear. This patch allows one of the other UARTs to be
selected in the kernel configuration. It is assumed that the
bootloader has configured and initialized the UART since this was the
previous assumption.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>