[IRDA]: Switching to a workqueue for the SIR work

Since sir_kthread.c pretty much duplicates the workqueue
functionality, we'd better switch.  The SIR fsm has been merged into
sir_dev.c and thus sir_kthread.c is deleted.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Samuel Ortiz <samuel.ortiz@nokia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>