ARM: ux500: define serial port aliases

This enumerates the PL011 serial ports on the Ux500. This is
necessary to do if we want to remove one of the serial ports,
since userspace depends on console to be present on ttyAMA2
and we must not break userspace.

Cc: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Olof Johansson <olof@lixom.net>