Some board have multiple configurations.
For example, the board "m54455evb" has many configurations:
M54455EVB, M54455EVB_a66, M54455EVB_i66, M54455EVB_intel, ...

When we modify board-related files, we need to test
all configurations based on such a board.

In such a case, the new option -b is useful.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>