Bug#913523: workaround/fix: add more uefi syslinux files

[Carl Karsten <carl@nextdayvideo.com>]

This works for the one box I am testing on (the same OP's turbot).

There may be more files than needed, we were guessing and stopped when
it booted.

This suggests the existing boot.img can be fixed without breaking
backwards compatibility.

Get the syslinux package

dd boot.img /dev/sdX, mount /dev/sdX di

mkdir -p di/efi/boot

mv di/syslinux.cfg di/boot
cp efi64/efi/syslinux.efi di/efi/boot/bootx64.efi
cp di/efi/boot/syslinux.cfg di/efi/syslinux/syslinux.cfg
cp di/linux di/efi/boot/
cp di/initrd.gz di/efi/boot/

resulting files:

Unsure which files are needed in efi/boot and which ones are needed in
efi/syslinux

di/efi/
di/efi/boot
di/efi/boot/bootx64.efi
di/efi/boot/libutil.c32
di/efi/boot/menu.c32
di/efi/boot/ldlinux.e64
di/efi/boot/syslinux.cfg
di/efi/syslinux
di/efi/syslinux/menu.c32
di/efi/syslinux/ldlinux.e64
di/efi/syslinux/libutil.c32
di/efi/syslinux/syslinux.cfg