ARM: SAMSUNG: Fix mask value for S5P64X0 CPU IDs

The current value for S5P64XX_CPU_MASK does not include the necessary
bits, which causes detection failure.

Signed-off-by: Ajay Kumar <ajaykumar.rs@samsung.com>
[kgene.kim@samsung.com: changed the value]
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>