ARM: S3C24XX: move plat-s3c24xx/dev-uart.c into common.c

The uart devices are used on all s3c24xx machines, so they can reside
in the common code for all machines.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>