decouple Jehanne from 9P2000 (as much as needed)

Jehanne is going to use a new file protocol, but Plan 9 is really
coupled with 9P2000.

Renamed fcall.h as 9P2000.h and introduced specific constants such
as NP_OREAD, NP_OWRITE and so on, so that we can use different values
in the kernel and new protocol.

Renamed devmnt to devninep, since it's actually a device serving 9P2000
file systems.

Also, fixed 9P2000 support in Jehanne, that was broken with the introduction
of OSTAT.

sys/src/kern/boot/bootauth.c

@@ -10,7 +10,7 @@
 #include <u.h>
 #include <libc.h>
 #include <auth.h>
-#include <fcall.h>
+#include <9P2000.h>
 #include "../boot/boot.h"
 
 char	*authaddr;
@@ -56,7 +56,7 @@ authentication(int cpuflag)
 	}
 
 	/* wait for agent to really be there */
-	while(access("/mnt/factotum", 0) < 0)
+	while(access("/mnt/factotum", AEXIST) < 0)
 		sleep(250);
 
 	if(cpuflag)