WIP: xtensa: add dynamic tracing support

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
WIP: xtensa: deliver signal raised in double exception handler

This fixes infinite loop in the kernel on userspace access to unaligned
address in unmapped memory region.

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