mips.md: Complete the unfinished R4000 multiply/shift errata workaround.

	* config/mips/mips.md: Complete the unfinished R4000
	multiply/shift errata workaround.  Improve documentation.
	(hazard): Use TARGET_FIX_R4000 to decide whether an "imul" instruction
	has a hilo hazard.
	(mulsi3, mulsi3_internal, mulsi3_r4000): Use TARGET_FIX_R4000.
	(muldi3, muldi3_internal): Likewise.
	(muldi3_internal2): Remove, replacing with...
	(muldi3_mult3, muldi3_r4000): ...these new patterns.
	(mulsidi3): Take the errata into account.
	(mulsidi3_32bit): Remove, replacing with...
	(mulsidi3_32bit_internal, mulsidi3_32bit_r4000): ...these new patterns.
	(mulsidi3_64bit, mulsidi3_64bit_parts): Disable if TARGET_FIX_R4000.
	(umulsidi3): Take the errata into account.
	(umulsidi3_32bit): Remove, replacing with..
	(umulsidi3_32bit_internal, umulsidi3_32bit_r4000): ...these patterns.
	(umulsi3_highpart, umulsi3_highpart_internal): Disable if
	TARGET_FIX_R4000.
	(smulsi3_highpart, smulsi3_highpart_internal): Likewise.
	(smuldi3_highpart, umuldi3_highpart): Likewise.
	* doc/invoke.texi: Document the errata workaround.

From-SVN: r78622