ARM: S3C2416: Add armdiv_mask constant

The S3C2416/2450 has only 3 bits for the armdiv setting instead
of the 4 bits of the S3C2443.

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