tidy up the treatment of maxsysargs for the proc structure.  this really needs to
stay in port.  it is not architecture specific at all.

Reference: /n/atom/patch/applied/maxsysargtidy
Date: Sun Aug 16 06:08:10 CES 2015
Signed-off-by: quanstro@quanstro.net

--- /sys/src/nix/k10/dat.h	Sun Aug 16 06:07:45 2015
+++ /sys/src/nix/k10/dat.h	Sun Aug 16 06:07:46 2015
@@ -22,8 +22,6 @@
 #pragma incomplete Ureg
 #pragma incomplete Pcidev
 
-#define MAXSYSARG	5	/* for mount(fd, afd, mpt, flag, arg) */
-
 /*
  *  parameters for sysproc.c
  */
--- /sys/src/nix/port/portdat.h	Sun Aug 16 06:07:49 2015
+++ /sys/src/nix/port/portdat.h	Sun Aug 16 06:07:51 2015
@@ -695,6 +695,10 @@
 	vlong	vl;
 };
 
+enum {
+	Maxsysarg	= 5	/* for mount(fd, afd, mpt, flag, arg) */
+};
+
 struct Proc
 {
 	Label	sched;		/* known to l.s */
@@ -778,7 +782,7 @@
 	void	*kparg;
 
 	int	scallnr;	/* system call number */
-	uchar	arg[MAXSYSARG*sizeof(void*)];	/* system call arguments */
+	uchar	arg[Maxsysarg*sizeof(void*)];	/* system call arguments */
 	int	nerrlab;
 	Label	errlab[NERR];
 	char	*syserrstr;	/* last error from a system call, errbuf0 or 1 */