sunvdc: Add support for setting physical sector size

Physical sector size is supported in v1.2 of the vDisk protocol and
should be set if available.  If protocol version 1.2 is used and the
physical disk size is unavailable, then the disk is considered busy.

Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>