update mkfile.proto (include power64)

Reference: /n/atom/patch/applied2013/mkprotop64
Date: Wed Jun 19 16:40:19 CES 2013
Signed-off-by: quanstro@quanstro.net

--- /sys/src/mkfile.proto	Wed Jun 19 16:40:13 2013
+++ /sys/src/mkfile.proto	Wed Jun 19 16:40:13 2013
@@ -4,7 +4,7 @@
 
 OS=56789qv	#12k
 CPUS=amd64 arm 386
-#CPUS=arm alpha 386 amd64 power mips
+#CPUS=arm alpha 386 amd64 power power64 mips
 CFLAGS=-FTVw
 LEX=lex
 YACC=yacc