WIP: target-xtensa: add MX interrupt distributor

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
target-xtensa: improve spin locking performance

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
target-xtensa: WIP: support icount

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
target-xtensa: add MX support to sim machine

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
target-xtensa: add SMP tests

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
target-xtensa: refactor CCOUNT/CCOMPARE

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>