i386: Fix dot_prod backend patterns for mmx and sse targets

Following the migration of the dot_prod optab from a direct to a
conversion-type optab, ensure all back-end patterns incorporate the
second machine mode into pattern names.

gcc/ChangeLog:

	* config/i386/mmx.md (usdot_prodv8qi): Renamed to...
	(usdot_prodv2siv8qi): ...this.
	(sdot_prodv8qi): Renamed to...
	(sdot_prodv2siv8qi): ...this.
	(udot_prodv8qi): Renamed to...
	(udot_prodv2siv8qi): ...this.
	(usdot_prodv4hi): Renamed to...
	(usdot_prodv2siv4hi): ...this.
	(udot_prodv4hi): Renamed to...
	(udot_prodv2siv4hi): ...this.
	(sdot_prodv4hi): Renamed to...
	(sdot_prodv2siv4hi): ...this.
	* config/i386/sse.md (sdot_prod<mode>): Renamed to...
	(sdot_prod<sseunpackmodelower><mode>): ...this.
	(sdot_prodv4si): Renamed to...
	(sdot_prodv2div4si): ...this.
	(usdot_prod<mode>): Renamed to...
	(usdot_prod<ssedvecmodelower><mode>): ...this.
	(sdot_prod<mode>): Renamed to...
	(sdot_prod<ssedvecmodelower><mode>): ...this.
	(sdot_prodv64qi): Renamed to...
	(sdot_prodv16siv64qi): ...this.
	(udot_prod<mode>): Renamed to...
	(udot_prod<ssedvecmodelower><mode>): ...this.
	(udot_prodv64qi): Renamed to...
	(udot_prodv16qiv64qi): ...this.
	(usdot_prod<mode>): Renamed to...
	(usdot_prod<sseunpackmodelower><mode>): ...this.
	(udot_prod<mode>): Renamed to...
	(udot_prod<sseunpackmodelower><mode>): ...this.