mkinitfs: add zFCP SCSI device as root disk on s390x
Similar to DASD and QETH devices.
Example of kernel argument for 2 device paths: zfcp=0.0.1905:0x50050763070845e3:0x4082400400000000,0.0.1945:0x50050763071845e3:0x4082400400000000
Each device path is separated by a comma (,). Adapter bus ID and WWPNs and LUNs are separated by a colon (:).
Since Alpine has the advantage of using root=UUID= for root disk, device order and device naming don't matter.