py/obj: Optimise mp_obj_get_type for immediate objs with repr A and C.
py/obj: Optimise mp_obj_get_type for immediate objs with repr A and C.

This function is called often and with immediate objects enabled it has
more cases, so optimise it for speed.  With this optimisation the runtime
is now slightly faster with immediate objects enabled than with them
disabled.

pfalcon/micropython,pfalcon/micropython,pfalcon/micropython,pfalcon/micropython,pfalcon/micropython