arm: move flush_dcache_all() to just before disable cache

In Cortex-A15 architecture, when we run cache invalidate
the cache clean operation executes automatically.
So if there are any dirty cache lines before disabling the L2 cache
these will be synchronized with the main memory when
invalidate_dcache_all() runs in the last part of U-boot

The two functions after flush_dcache_all is using the stack. So this
data will be on the cache. After disable when invalidate is called the
data will be flushed from cache to memory. This corrupts the stack in
invalida_dcache_all. So this change is required to avoid the u-boot
hang.

So flush has to be done just before clearing CR_C bit

Signed-off-by: Arun Mankuzhi <arun.m@samsung.com>
Signed-off-by: Simon Glass <sjg@chromium.org>