Revert r183628 as with the current ata(4) ATAPI DMA with AcerLabs

M5229 appears to be once again fixed. If this happens to return
we probably should disable ATAPI DMA in ataacerlabs(4) instead
just like the Linux libATA does.

sys/boot/sparc64/loader/main.c

@@ -261,7 +261,6 @@ static int
 sparc64_autoload(void)
 {
 
-	setenv("hw.ata.atapi_dma", "0", 0);
 	return (0);
 }