arm64: Mark all I/O as non-secure shared

All I/O is by default considered non-secure for realms. As such
mark them as shared with the host.

Co-developed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Steven Price <steven.price@arm.com>