support for david's steamroller

Reference: /n/atom/patch/applied/steamrollhz
Date: Mon Apr  7 23:20:25 CES 2014
Signed-off-by: quanstro@quanstro.net

--- /sys/src/nix/k10/archk10.c	Mon Apr  7 23:20:25 2014
+++ /sys/src/nix/k10/archk10.c	Mon Apr  7 23:20:25 2014
@@ -120,6 +120,7 @@
 		case 0x00100f40:		/* phenom ii x4 */
 		case 0x00100f90:		/* K10 */
 		case 0x00000620:		/* QEMU64 */
+		case 0x00600f20:		 /* steamroller fx-8320 */
 			msr = rdmsr(0xc0010064);
 			r = (msr>>6) & 0x07;
 			hz = (((msr & 0x3f)+0x10)*100000000ll)/(1<<r);