allow acpi to disable legacy bits like keyboards, vga, etc.

Reference: /n/atom/patch/applied2013/nixiapcbootarch
Date: Sat Oct  5 17:41:11 CES 2013
Signed-off-by: quanstro@quanstro.net

--- /sys/src/nix/k10/devacpi.c	Sat Oct  5 17:40:48 2013
+++ /sys/src/nix/k10/devacpi.c	Sat Oct  5 17:40:48 2013
@@ -1509,6 +1509,28 @@
 		ioalloc(addr, len, 0, "acpi");
 }
 
+enum {
+	Blegacy		= 1<<0,
+	B8042kbd	= 1<<1,
+	Bnovga		= 1<<2,
+	Bnomsi		= 1<<3,
+	Bnocmos	= 1<<4,
+};
+
+static void
+iapcbootarch(void)
+{
+	int i;
+
+	i = fadt.iapcbootarch;
+
+	sys->nolegacyprobe = !(i&Blegacy);
+	sys->noi8042kbd = !(i&B8042kbd);
+	sys->novga = i&Bnovga;
+	sys->nomsi = i&Bnomsi;
+	sys->nocmos = i&Bnocmos;
+}
+
 int
 devacpiinit(void)
 {
@@ -1517,6 +1539,7 @@
 		acpirsdptr();
 		if(fadt.smicmd == 0)
 			return -1;
+		iapcbootarch();
 	}
 	return 0;
 }
@@ -1530,8 +1553,10 @@
 	 * This was written for the stock kernel.
 	 * This code must use 64 registers to be acpi ready in nix.
 	 */
-	if(1 || devacpiinit() < 0)
+	if(devacpiinit() < 0)
 		error("no acpi");
+
+	error("acpi disabled");
 
 	/*
 	 * should use fadt->xpm* and fadt->xgpe* registers for 64 bits.