kunit: rename base KUNIT_ASSERTION macro to _KUNIT_FAILED

Context:
Currently this macro's name, KUNIT_ASSERTION conflicts with the name of
an enum whose values are {KUNIT_EXPECTATION, KUNIT_ASSERTION}.

It's hard to think of a better name for the enum, so rename this macro.
It's also a bit strange that the macro might do nothing depending on the
boolean argument `pass`. Why not have callers check themselves?

This patch:
Moves the pass/fail checking into the callers of KUNIT_ASSERTION, so now
we only call it when the check has failed.
Then we rename the macro the _KUNIT_FAILED() to reflect the new
semantics.

Signed-off-by: Daniel Latypov <dlatypov@google.com>
Reviewed-by: David Gow <davidgow@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>