This was a very early test and got bitrotten inside a esp32-only
whitelist. Make it run generically.
SMP must be forced off by the test (it's commonly a platform default).
Add a build-time failure when the configuration is single-CPU, for
clarity.
Filter the test likewise so it runs on all supported systems.
Also, the key argument to the CPU startup function is vestigial and
the test was being too strict by requiring it to be non-zero.
Finally, the qemu command line needs to predicate the "-smp" argument
on CONFIG_MP_NUM_CPUS and not just CONFIG_SMP so we have an extra CPU
to test against.
Signed-off-by: Andy Ross <andrew.j.ross@intel.com>
