CSKY: Change mvtc and mulsw's ISA flag.

gas/
	* config/tc-csky.c (CSKYV2_ISA_DSP): CSKY_ISA_DSPE60.
	(CSKY_ISA_860): Likewise.

include/
	* opcode/csky.h (CSKY_ISA_DSPE60): Define.

opcodes/
	* csky-opc.h (csky_v2_opcodes): Change mvtc and mulsw's
	ISA flag.