pc64: use unsigned long for kmapindex and mmu counts avoiding signed integer division

sys/src/9/pc64/dat.h

@@ -141,9 +141,9 @@ struct PMMU
 	MMU*	mmutail;
 	MMU*	kmaphead;
 	MMU*	kmaptail;
-	int	kmapcount;
-	int	kmapindex;
-	int	mmucount;
+	ulong	kmapcount;
+	ulong	kmapindex;
+	ulong	mmucount;
 };
 
 /*
@@ -182,7 +182,7 @@ struct Mach
 
 	u64int	mmumap[4];		/* bitmap of pml4 entries for zapping */
 	MMU*	mmufree;		/* freelist for MMU structures */
-	int	mmucount;		/* number of MMU structures in freelist */
+	ulong	mmucount;		/* number of MMU structures in freelist */
 
 	ulong	ticks;			/* of the clock since boot time */
 	Label	sched;			/* scheduler wakeup */

sys/src/9/pc64/mmu.c

@@ -27,8 +27,8 @@ static struct {
 	Lock;
 	MMU	*free;
 
-	int	nalloc;
-	int	nfree;
+	ulong	nalloc;
+	ulong	nfree;
 } mmupool;
 
 /* level */