ARM: debug: add support for Palmchip BK-310x UART

Some SoCs use a Palmchip BK-310x UART which is mostly 16550 compatible
but with a different register layout. While this UART has previously
only been supported in MIPS based chips (Alchemy, Ralink), the ARM based
SMP87xx series from Sigma Designs also uses it.

This patch allows the debug console to work with this type of UART.

Signed-off-by: Mans Rullgard <mans@mansr.com>
Signed-off-by: Marc Gonzalez <marc_gonzalez@sigmadesigns.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Olof Johansson <olof@lixom.net>