ARM: EXYNOS: Constify clksrc immutable register restore tables

The clksrc tables are constant, they are not used to store register values
at suspend.

size arch/arm/mach-exynos/pm.o
   text	   data	    bss
   1591	    212	     12	   // Before
   1671	    132	     12	   // After

Signed-off-by: Daniel Kurtz <djkurtz@chromium.org>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>