basic support for configuration given by acpi.  enable this for
msi.

Reference: /n/atom/patch/applied2013/nixcarefulprobe
Date: Sat Oct  5 10:37:04 CES 2013
Signed-off-by: quanstro@quanstro.net

--- /sys/src/nix/k10/dat.h	Sat Oct  5 10:36:13 2013
+++ /sys/src/nix/k10/dat.h	Sat Oct  5 10:36:13 2013
@@ -217,10 +217,10 @@
 
 	union {
 		struct {
-			uintmem	pmstart;	/* physical memory */
+			uintmem	pmstart;		/* physical memory */
 			uintmem	pmend;		/* total span */
 
-			uintptr	vmstart;	/* base address for malloc */
+			uintptr	vmstart;		/* base address for malloc */
 			uintptr	vmunused;	/* 1st unused va */
 			uintptr	vmunmapped;	/* 1st unmapped va */
 			uintptr	vmend;		/* 1st unusable va */
@@ -229,12 +229,20 @@
 
 			uint	copymode;	/* 0 is copy on write, 1 is copy on reference */
 
+			uchar	legacyprobe;	/* acpi tells us */
+			uchar	i8042kbd;
+			uchar	novga;
+			uchar	nomsi;
+			uchar	nocmos;
+
+			uchar	monitor;
+
 			uvlong	npages;		/* total physical pages of memory */
 			uvlong	upages;		/* user page pool */
 			uvlong	kpages;		/* kernel pages */
 
 			u64int	epoch;		/* crude time synchronisation */
-			ulong	ticks;			/* of the clock since boot time */
+			ulong	ticks;		/* of the clock since boot time */
 		};
 		uchar	syspage[4*KiB];
 	};
--- /sys/src/nix/k10/msi.c	Sat Oct  5 10:36:14 2013
+++ /sys/src/nix/k10/msi.c	Sat Oct  5 10:36:15 2013
@@ -65,6 +65,9 @@
 	char *s;
 	uint c, f, d, datao, lopri, dmode, logical;
 
+	if(sys->nomsi)
+		return -1;
+
 	c = msicap(p);
 	if(c == 0)
 		return -1;