cpuid: Don't test 486 and pentium with TCG

The CPUID test kernel uses CMOV, pentium and 486 don't have it enabled,
and the test kernel will crash. Skip those CPu models by now.

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
cpuid: Try to test everything by default

Instead of skipping test cases when the QEMU version or host CPU is
unknown, try to test everything. Unavailable CPU models and
machine-types will generate a SKIP test result, anyway.

There are 473 qemu_cpu test cases, and most of them take around 3
seconds to run.

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>