* simplify and clean the attach code a lot, and support the 'drive'
locator
* pass proper dev_t to readdisklabel() - formerly, the passed value was
completely broken (used incorrect major and wrong minor), but worked
by accident
* worker thread is now spawned per controller, rather than per-drive;
i/o cannot be done concurrently by different drivers, only one
i/o can be pending at any time
* simplify the command queue code, just sleep appropriately when
!poll case, g/c 'async' code formerly needed, move the bio code
from ed_mca.c to edc_mca.c:edc_bio()
* other misc cleanups
and for initial autoconf probes; the latter eliminates need for
deferred configuration (and makes dmesg a bit nicer).
g/c EDF_IODONE flag - protect against interrupt by calling tsleep()
at splbio in worker thread
g/c unneeded stuff, improve some autoconf messages
to be cleared always in edmcadone(), otherwise if there is a write
via bounce buffer followed by read directly to buf, the read operation
would return trashed data (the buf data would get overwritten
by contents of bounce buffer in edmcadone()).
Reset b_resid as necessary when the i/o is done, too.
g/c some unneeded stuff, use lockmgr()-style locking in ed_[un]lock(),
better avoid some deadlocks
These changes make the driver quite a bit more stable. It's actually
reliable enough to be possible to newfs the drive and use it for
read/write filesystem now.
