Certain levels of IBM firmware will allow the system to boot from an

iscsi target.  System OFW accomplishes this by setting up a virtual
disk device with parameters.  These parameters, when passed back to
OFW by yaboot, directs the FW to use virtual device over the ethernet
port that will then access iscsi target as a block device.  This patch
extracts those parameters from the property of the virtual device and
passes them back to OFW to indicate the kernel is to be retrieved via
the iscsi protocol.

Signed-off-by: Doug Maxey <dwm@austin.ibm.com>
Cc: Ben Herrenscmidt <benh@kernel.crashing.org>
Cc: Mike Christie <michaelc@cs.wisc.edu>