ARM: BCM63XX: add low-level UART debug support

Broadcom BCM63xx DSL SoCs have a different UART implementation for which
we need specially crafted low-level debug assembly code to support. Add
support for this using the standard definitions provided in
include/linux/serial_bcm63xx.h (shared with their MIPS counterparts).

Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>