kselftest: Add mechanism for reporting a KSFT_ result code

kselftest: Add mechanism for reporting a KSFT_ result code

Currently there's no helper which a test can use to report it's result as
a KSFT_ result code, we can report a boolean pass/fail but not a skip. This
is sometimes a useful idiom so let's add a helper ksft_test_result_report()
which translates into the relevant report types.

Due to the use of va_args in the result reporting functions this is done as
a macro rather than an inline function as one might expect, none of the
alternatives looked particularly great.

Resolved merge conflict in next betwwen the following commits:
f7d5bcd35d42 ("selftests: kselftest: Mark functions that unconditionally call exit() as __noreturn")

5d3a9274f0d1 ("kselftest: Add mechanism for reporting a KSFT_ result code")

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Shuah Khan <skhan@linuxfoundation.org>

Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>