kernel - Remove unnecessary mplock from ata I/O path
* ata_finish() doesn't need the MP Lock; moving it from taskqueue_swi
to taskqueue_swi_mp will make sure it's not taken.
* Note that taskqueue_swi(_mp) will be processed when this ithread
attempts to switch back to the thread it preempted. This means that
taskqueue_swi(_mp) processing exclude processing further interrupts
on the ithread while they're running. This may not be desirable and
is different than taskqueue_swi / swi_* / setsoft* in FreeBSD 4.x.
Submitted-by: vsrinivas