MIPS: Fix generation of Loongson-specific division and modulo instructions.

gcc

	* config/mips/mips.h (ISA_HAS_DIV3): Remove unused macro.
	(ISA_AVOID_DIV_HILO): New macro.
	(ISA_HAS_DIV): Use new ISA_AVOID_DIV_HILO macro.
	(ISA_HAS_DDIV): Likewise.

From-SVN: r244570