i440fx-test: Fix test paths to include architecture

Replace g_test_add_func() with new qtest_add_func() and g_test_add()
macro with qtest_add() macro. This effectively changes GTester paths:

  /i440fx/foo -> /x86_64/i440fx/foo etc.

Cc: qemu-stable@nongnu.org
Reviewed-by: John Snow <jsnow@redhat.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>