tests/bios-tables-test: Fix endianess problems when passing data to iasl

tests/bios-tables-test: Fix endianess problems when passing data to iasl

The bios-tables-test was writing out files that we pass to iasl in
with the wrong endianness in the header when running on a big endian
host. So instead of storing mixed endian information in our structures,
let's keep everything in little endian and byte-swap it only when we
need a value in the code.

Reported-by: Daniel P. Berrange <berrange@redhat.com>
Buglink: https://bugs.launchpad.net/qemu/+bug/1724570
Suggested-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
Tested-by: "Daniel P. Berrange" <berrange@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>