ieee1275: set-address bus specific method

ieee1275: set-address bus specific method

IEEE 1275-1994 Standard for Boot (Initialization Configuration)
Firmware: Core Requirements and Practices
E.3.2.2 Bus-specific methods for bus nodes

A package implementing the scsi-2 device type shall implement the
following bus-specific method:

 set-address ( unit# target# -- )
   Sets the SCSI target number (0x0..0xf) and unit number (0..7) to which
   subsequent commands apply.

This function is for devices with #address-cells == 2

Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>