[RESEND V3] ieee1275/ofdisk: vscsi lun handling on lun len

The information about "vscsi-report-luns" data is a list of disk details with pairs of memory addresses and lengths. 8 bytes 8 bytes lun-addr ---> 8 bytes ^| buf-addr | lun-count| > - |

[RESEND V6] ieee1275/ofdisk: retry on open and read failure

Sometimes, when booting from a very busy SAN, the access to the disk can fail and then GRUB will eventually drop to GRUB prompt. This scenario is more frequent when deploying many machines at the same time using the same SAN. This patch aims to force the ofdisk module to retry the open or read func