ARM: 8257/1: OMAP2+: use common l2cache initialization code

This patch implements generic DT L2C initialisation (the one from
init_IRQ in arch/arm/kernel/irq.c) for Omap4 and AM43 platforms and
kills the SoC specific stuff in arch/arm/mach-omap2/omap4-common.c.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Tested-by: Nishanth Menon <nm@ti.com>
Acked-by: Nishanth Menon <nm@ti.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>