smbios: Default all values to zero.

Make sure to initialize the entire smbios area to zero so that any
field not explicitly initialized does not have random values.  (It was
found that the memory_error_information_handle field in smbios_type_17
was not being set.)

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
init_virtio_blk, init_virtio_scsi: reset HBA on error

Extend commit 5f2d17d35b2339526f3b3d580b279ea78e406a25: reset on all error
paths, and also for virtio_blk not just virtio_scsi.

Signed-off-by: Eric Northup <digitaleric@google.com>
vp_init_simple: enable PCI bus-mastering before relying on DMA.

An analogous change was made in the LSI scsi driver, commit
7d052575258ad2fc487ca3f9a6b62eff1b767900. Qemu works around guests that don't
correctly enable PCI bus mastering before using virtio queues' DMA (search for
VIRTIO_PCI_BUG_BUS_MASTER / VIRTIO_PCI_FLAG_BUS_MASTER_BUG ), but it'd be
better to be correct.

Signed-off-by: Eric Northup <digitaleric@google.com>