Support addr=... in option argument of -drive if=virtio

Support addr=... in option argument of -drive if=virtio

Make drive_init() accept addr=, put the value into struct DriveInfo.
Use it in all the places that create virtio-blk-pci devices:
pc_init1(), bamboo_init(), mpc8544ds_init().

Don't support addr= in third argument of monitor command pci_add and
second argument of drive_add, because that clashes with their first
arguments.  Admittedly unelegant.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>