set the arch in the tdl to be compatibile with qemu
as 32 bit arm can run hardware or software floating point code,
we have a bunch of arches that are not exactly real to
differenciate and keep installs sane. qemu only understands
armv7l, so we need to always use armv7l for virt on 32 bit arm
Signed-off-by: Dennis Gilmore <dennis@ausil.us>