ARM: S5P6440: Add serial port support

This patch adds UART serial port support for S5P6440 CPU. Most of the
serial support of Samsung's 6400 CPU is reused for 6440 CPU.

Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>
Signed-off-by: Ben Dooks <ben-linux@fluff.org>