serial: 8250_dw: Add support for big-endian MMIO accesses

Add support for UPIO_MEM32BE in addition to UPIO_MEM32.

For big endian we use 2 new accessors similar to little endian,
called dw8250_serial_out32be() and dw8250_serial_in32be().

Signed-off-by: Noam Camus <noamc@ezchip.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>