ARM: EXYNOS: Constify data tables for pmu

These tables are all immutable, make them const to save 4416 bytes of RAM.

size arch/arm/mach-exynos/pmu.o
   text	   data	    bss
    848	   4420	      4		// before
   5264	      4	      4		// after

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