omap4: Unconditionally require l2x0 L2 cache controller support

If running in the Normal World on a TrustZone-enabled SoC, Linux
does not have complete control over the L2 cache controller
configuration.  The kernel cannot work reliably on such platforms
without the l2x0 cache support code built in.

This patch unconditionally enables l2x0 support for the OMAP4 SoCs.

Thanks to Rob Herring for this suggestion.  [1]

[1] http://lists.infradead.org/pipermail/linux-arm-kernel/2011-November/074495.html

Signed-off-by: Dave Martin <dave.martin@linaro.org>
Acked-by: Tony Lindgren <tony@atomide.com>