arm64: smp: Undo flushing of caches from local_cpu_stop

Upon a panic, the cache flushes are handled by the software
layers that collect the ramdumps. Hence doing it from the
kernel is no longer necessary and can be removed.

Change-Id: I83860fb4361e42aea69f0f5cc75aaff5c3c4e3b0
Signed-off-by: Raghavendra Rao Ananta <rananta@codeaurora.org>