Update PCI drivers to no longer look at the MEMIO-enabled bit in the PCI
command register.  The lazy BAR allocation code in FreeBSD sometimes
disables this bit when it detects a range conflict, and will re-enable
it on demand when a driver allocates the BAR.  Thus, the bit is no longer
a reliable indication of capability, and should not be checked.  This
results in the elimination of a lot of code from drivers, and also gives
the opportunity to simplify a lot of drivers to use a helper API to set
the busmaster enable bit.

This changes fixes some recent reports of disk controllers and their
associated drives/enclosures disappearing during boot.

Submitted by:	jhb
Reviewed by:	jfv, marius, achadd, achim
MFC after:	1 day
Alter the mq_start routine to do a TRYLOCK and call to the locked routine
rather than just queueing. The former code was an attempt at getting
UDP performance up, but there have been customer reports of problems with it,
so the ixgbe approach seems the best solution for now.