Disabling the L2 cache is not working in imx5_init_lowlevel() because
the necessary cache maintenance operations are missing. This often
results in cache corruption in a chainloaded barebox.
Disabling the cache is unnecessary: when we come from the ROM the L2
cache is disabled anyway, so disabling it is a no-op. When we get here
in a chainloaded barebox the L2 cache is already enabled and correctly
configured. So instead of initializing it again we can take an enabled
L2 cache as a sign to skip initialization and just return from the
function.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>