omap4: l2x0: Override the default l2x0_disable

The machine_kexec() calls outer_disable which can crash on OMAP4
becasue of trustzone restrictions.

This patch overrides the default l2x0_disable with a OMAP4
specific implementation taking care of trustzone

Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Reviewed-by: Tony Lindgren <tony@atomide.com>
Acked-by: Linus Walleij <linus.walleij@stericsson.com>