ARM: EXYNOS: Remove legacy PMU initialization code

This patch removes legacy PMU initialization code that was used to set
up PMU when booting with ATAGS, which is not supported any more.

Signed-off-by: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>