USB: f81232: implement read IIR/MSR with endpoint

The interrupt endpoint will report current IIR. If we got IIR with MSR changed
, We will do read MSR with interrupt_work worker to do f81232_read_msr()
function.

Signed-off-by: Peter Hung <hpeter+linux_kernel@gmail.com>
Signed-off-by: Johan Hovold <johan@kernel.org>