ARM: add Marvell Berlin UART0 lowlevel debug

This adds UART0 as found on Marvell 88DE3xxx SoCs, e.g. Armada 1500
to the list of possible lowlevel debug options.

Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Reviewed-by: Jason Cooper <jason@lakedaemon.net>
Reviewed-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>