test: Support testing with two board-builds

test: Support testing with two board-builds

The Beagleplay board uses an SoC from the TI K3 family. This has both a
Cortex-R core and a Cortex-A core and the R core needs to come up before
the A core. In both cases we have U-Boot SPL then U-Boot proper being
used.

In practice this means we need two entirely separate builds to produce
an image.

Handle this in test.py by adding more parameters.

Signed-off-by: Simon Glass <sjg@chromium.org>