buildman: Fix up tests

The tests were broken by two separate commits which adjusted the output
when boards are listed. Fix this by adding back a PowerPC board and
putting the name of each board in the test.

Fixes: b9f7d881 (powerpc, 5xx: remove some "5xx" remains)
Fixes: 8d7523c5 (buildman: Allow showing the list of boards with -n)

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