MFC r329268, r329517
r329268:
efi: Only scan the BLKIO MEDIA once
Scan only the BLOCK IO MEDIA once instead of each time for each type of
device (fd, cd and hdd).
Leave the mechanism to free and reprobe all devices if one day we want
to implement a "dev rescan" thing.
r329517:
efi: Do not pad the efi devpath structure
This solve problem when booting with efi on armv7