ARM: zynq: Fix earlyprintk in big endian mode

earlyprintk messages are not appearing on the terminal
emulator during a big endian kernel boot. In BE mode
sending full words to UART will result in unprintable
characters as they are byte swapped versions of printable
ones. So send only bytes.

Signed-off-by: Arun Chandran <achandran@mvista.com>
Tested-by: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>