cmd/7g: teach 7g/prog.c about UMULL

Fixes

/home/dfc/go.arm64/src/runtime/alg.go:97: internal compiler error: proginfo: unknown instruction 00057 (/home/dfc/go.arm64/src/runtime/alg.go:92)       UMULL   R10,R9

Author: davecheney

src/cmd/7g/prog.c

@@ -44,6 +44,7 @@ static ProgInfo progtable[ALAST] = {
 	[AORR]=		{SizeQ | LeftRead | RegRead | RightWrite},
 	[AEOR]=		{SizeQ | LeftRead | RegRead | RightWrite},
 	[ASMULL]=	{SizeQ | LeftRead | RegRead | RightWrite},
+	[AUMULL]=	{SizeQ | LeftRead | RegRead | RightWrite},
 	[ASMULH]=	{SizeL | LeftRead | RegRead | RightWrite},
 	[AUMULH]=	{SizeL | LeftRead | RegRead | RightWrite},
 	[ASDIV]=	{SizeQ | LeftRead | RegRead | RightWrite},