powerpc/fsl-booke: Enable L1 cache on e500v1/e500v2/e500mc CPUs

Some boot loaders may not enable L1 instruction/data cache.  Check if
data and instruction caches are enabled, and enable them if needed.

Signed-off-by: Nate Case <ncase@xes-inc.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>