instead of including kernel and config in the efi
fat image, we can just include the loaders and
read the plan9.ini and kernel from iso filesystem
just like the bios loaders.
having the memconf() (*e820=) last clutters the screen.
do it first, so we can read *acpi= and *bootscreen=
prints.
we want to continue using tftp even when the /cfg/pxe/$ether
file is not found. only when we detect no pxe/dhcp session,
then we switch to local filesystem (non-network boot).
