rs6000: Add expand pattern for multiply-add (PR103109)

gcc/
	PR target/103109
	* config/rs6000/rs6000.md (<u>maddditi4): New pattern for multiply-add.
	(<u>madddi4_highpart): New.
	(<u>madddi4_highpart_le): New.

gcc/testsuite/
	PR target/103109
	* gcc.target/powerpc/pr103109.h: New.
	* gcc.target/powerpc/pr103109-1.c: New.
	* gcc.target/powerpc/pr103109-2.c: New.