Fix disassembly of RX zero-offset register indirect instructions.

Fix disassembly of RX zero-offset register indirect instructions.

opcode	* rx.h (enum RX_Operand_Type): Add RX_Operand_Zero_Indirect.

opcodes	* rx-decode.opc (rx_disp): If the displacement is zero, set the
	type to RX_Operand_Zero_Indirect.
	* rx-decode.c: Regenerate.
	* rx-dis (print_insn): Handle RX_Operand_Zero_Indirect.

gas	* config/rx-parse.y: Allow zero value for 5-bit displacements.

tests	* gas/rx/mov.sm: Add tests for zero offset indirect moves.
	* gas/rx/mov.d: Update expected output.