currently the EFI loader's behavior is to search all disks in a
firmware-defined order. we search the list returned by the firmware
in reverse order in the hopes of searching the first 9FAT instead of
the ESP, but this results in unintuitive behavior when there are
multiple FAT partitions (possibly in multiple disks), such as loading
a plan9.ini and kernel from a different disk than the one you executed
the EFI loader from.
to resolve this, we change the EFI loader to instead prefer read
plan9.ini and the kernel from the same disk as the EFI loader was read
from, and then fall back to the old behavior, since the old behavior
is relied on by current installations.
486ce60546