On sparc64 obtain the initiator ID to be used for SPI HBAs from the
Open Firmware device tree in order to match what the PROM built-in
driver uses. This is especially important when netbooting Fujitsu
Siemens PRIMEPOWER250 as in that case the built-in driver isn't used
and the port facts PortSCSIID defaults to 0, conflicting with the
disk at the same address.
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