armv7: omap3: leave outer cache enabled

Mainline kernel for OMAP3 doesn't enable L2 cache
It expects L2$ to be enabled by ROM-code/bootloader.

Leaving L2$ enabled can be troublesome in cases where
the L2 cache is not under CP15 control, such as in
Cortex-A9. This problem is explained in detail in
the commit dc7100f4



However, this problem doesn't apply to Cortex-A8
because L2$ in Cortex-A8 is under CP15 control and
hence the generic armv7 maintenance opertions work
for it.

As such we can make an exception for OMAP3 and
leave the L2$ enabled when we jump to kernel. This
is done by removing the strongly-linked implementation
of v7_outer_cache_disable() and allowing it to fall
back to the weakly linked implementation that doesn't
do anything.

Signed-off-by: Aneesh V <aneesh@ti.com>