work around not knowing the frequency of some amd chips.

amd chips tend to use a different set of msrs for each new arch,
and i'm not sure about the machine i'm trying to get up yet.
sometimes it involves picking around in extended pci registers.

so, i think this is the safest way to get the machine in question booting,
and we can work out what the best way forward from here is.

Reference: /n/atom/patch/applied/amdhzpanic
Date: Sat May 24 19:47:49 CES 2014
Signed-off-by: quanstro@quanstro.net

--- /sys/src/nix/k10/archk10.c	Sat May 24 19:44:53 2014
+++ /sys/src/nix/k10/archk10.c	Sat May 24 19:44:54 2014
@@ -110,7 +110,10 @@
 		cpuid(1, 0, info);
 		switch(info[0] & 0x0fff0ff0){
 		default:
-			return 0;
+			iprint("cpuidhz: BUG: HZ unknown for %.8ux: guess 2.8Ghz\n",
+				info[0] & 0x0fff0ff0);
+			hz = 2800000000;
+			break;
 		case 0x00000f50:		/* K8 */
 			msr = rdmsr(0xc0010042);
 			if(msr == 0)