ARM: 5917/1: OMAP4: Add L2 Cache support

This patch adds L2 Cache support for OMAP4. External L2 cache
is used in OMAP4

CC: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>