ARM: l2c: remove unnecessary call to outer_flush_all()

outer_disable() is defined to safely turn the L2 cache off without data
loss: this means that outer_flush_all() should never be called unless
you need to implement some special L2 cache disabling, and even then
only from your replacement L2 cache disable function.

Acked-by: Barry Song <Baohua.Song@csr.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>