Improve PCI BAR emulation:
- Respect the MEMEN and PORTEN bits in the command register
- Allow the guest to reprogram the address decoded by the BAR

Submitted by:	Gopakumar T
Obtained from:	NetApp
Change name of variable from 'rwlock' to more descriptive 'mmio_rwlock'

Requested by:	grehan
Obtained from:	NetApp