ARM: cache-v7: consolidate initialisation of cache level index

Both v7_flush_cache_louis and v7_flush_dcache_all both begin the
flush_levels loop with r10 initialised to zero.  In each case, this
is done immediately prior to entering the loop.  Branch to this
instruction in v7_flush_dcache_all from v7_flush_cache_louis and
eliminate the unnecessary initialisation in v7_flush_cache_louis.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>