test: qemu: add qfw sandbox driver, dm tests, qemu tests

A sandbox driver and test are added for the qfw uclass, and a test in
QEMU added for qfw functionality to confirm it doesn't break in real
world use.

Signed-off-by: Asherah Connor <ashe@kivikakk.ee>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>