ARM: EXYNOS: Add exynos5260 PMU compatible string to DT match table

Exynos initialisation code now relies on obtaining the PMU address via
DT, so add the exynos5260 PMU compatible string to DT match table.

Signed-off-by: Vikas Sajjan <vikas.sajjan@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>