Add dmamode.
 [jmk] --rw-rw-r-- M 107020 glenda sys 369 Nov 19 21:09 sys/lib/dist/pc/plan9.ini.cd
	/n/sourcesdump/2005/1119/plan9/sys/lib/dist/pc/plan9.ini.cd:9,14 - 
	/n/sourcesdump/2005/1120/plan9/sys/lib/dist/pc/plan9.ini.cd:9,15
	  mouseport=ask
	  monitor=ask
	  vgasize=ask
	+ dmamode=ask
	  adisk=/dev/sdD0/cdboot
	  cdboot=yes