ARM: EXYNOS: Remove legacy L2X0 initialization

Since Exynos is now supporting only DT-based boot, the old L2X0
initialization code is not needed anymore, so exynos4_l2x0_cache_init()
can be greatly simplified.

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