kunit: enable hardware acceleration when available

Use KVM or HVF if supported by the QEMU binary and available on the
system.

This produces a nice improvement on my Apple M3 Pro running macOS 14.7:

Before:
./tools/testing/kunit/kunit.py exec --arch arm64
[HH:MM:SS] Elapsed time: 10.145s

After:
./tools/testing/kunit/kunit.py exec --arch arm64
[HH:MM:SS] Elapsed time: 1.773s

Signed-off-by: Tamir Duberstein <tamird@gmail.com>
Reviewed-by: David Gow <davidgow@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>