ARM: 7957/1: add DSB after icache flush in __flush_icache_all()

commit 39544ac9df20f73e49fc6b9ac19ff533388c82c0 upstream.

Add DSB after icache flush to complete the cache maintenance operation.

Signed-off-by: Vinayak Kale <vkale@apm.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>