cmake: Fix how usage finds board names

We had been search for <BOARD>.yaml, however its possible that doesn't
match anything and we actually use <BOARD>_defconfig in
boilerplate.cmake.  So search for *_defconfig instead of *.yaml to
generate the <BOARD> list.

Signed-off-by: Kumar Gala <kumar.gala@linaro.org>
1 file changed