azure/gitlab: Add tests for SiFive Unleashed board

azure/gitlab: Add tests for SiFive Unleashed board

This adds CI tests for SiFive Unleashed board.

QEMU supports booting exact the same images as used on the real
hardware out of the box, that U-Boot SPL loads U-Boot proper
from either an SD card or the SPI NOR flash, hence we can easily
set up CI to cover these 2 boot flows of SiFive Unleashed board.

With this, now we can have regression testing of mmc-spi-slot and
sifive spi drivers, as well as mmc and spi-nor subsystems.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Tom Rini <trini@konsulko.com>