target-xtensa: add cpu3400 core

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
target-xtensa: add dsp3400 core

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
target-xtensa: provide GDB support for the fsf core

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