patchtest/selftest: add XSKIP, update test files

patchtest/selftest: add XSKIP, update test files

Since we are skipping the merge test, two of the selftests now report
SKIP instead of XPASS/XFAIL as expected. Adjust the two files to have
the right endings for XSKIP, and add the category so that it can be used
for more extensive testing in the future.

Signed-off-by: Trevor Gamblin <tgamblin@baylibre.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>