arm64: add DSB after icache flush in __flush_icache_all()

arm64: add DSB after icache flush in __flush_icache_all()

commit 5044bad43ee573d0b6d90e3ccb7a40c2c7d25eb4 upstream.

Add DSB after icache flush to complete the cache maintenance operation.
The function __flush_icache_all() is used only for user space mappings
and an ISB is not required because of an exception return before executing
user instructions. An exception return would behave like an ISB.

Signed-off-by: Vinayak Kale <vkale@apm.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>