arm64: io: Hook up __io_par() for inX() ordering

Ensure that inX() provides the same ordering guarantees as readX()
by hooking up __io_par() so that it maps directly to __iormb().

Reported-by: Andrew Murray <andrew.murray@arm.com>
Reviewed-by: Palmer Dabbelt <palmer@sifive.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>