tests/kernel/semaphore: Skip COHERENCE-hostile test cases

These two cases use a k_pipe to transfer data, and do it (as is
customary) by copying into or out of buffers on the stack.  But that
doesn't work when KERNEL_COHERENCE=y, because the pipe code has a
possibly-too-sophisticated zero copy implementation, and will do the
copy into the destination thread synchronously with the k_put_put()
call from the other CPU.

Normally the fix is to use a static buffer instead, but in this case
the buffers are shared between multiple simultaneous threads, so can't
be shared.

Just skip the tests, pending some rework to how they communicate.

Signed-off-by: Andy Ross <andrew.j.ross@intel.com>