sim: h8300 Fixed different behavior in preinc/predec.

* sim-main.h (h8_typecodes): Add operand type OP_REG_DEC, OP_REG_INC.
* compile.c (decode): Rewrite oprand type for specific case.
(fetch_1): Add handling OP_REG_DEC and OP_REG_INC.
(step_once): Fix operand fetch order.