py: Add ioctl method to stream protocol; add initial modselect.
stmhal: Implement generic select.select and select.poll.
stmhal: Add polling ability to UART object.
py: Rename mp_builtin_id to mp_obj_id and make it public.
stmhal: Fix modselect so non-hashable objects can be polled.
Remove skeletal modselect from extmod and just put it in stmhal.
stmhal: uart ioctl uses EINVAL, and checks TXE bit for write-ability.