Support constant TSC feature in future AMD CPUs.

Based on the documentation recently posted by Richard Brunner.

Index: linux/arch/x86_64/kernel/setup.c
===================================================================
--- linux.orig/arch/x86_64/kernel/setup.c
+++ linux/arch/x86_64/kernel/setup.c
@@ -872,6 +872,10 @@ static int __init init_amd(struct cpuinf
 		} 
 	} 
 	display_cacheinfo(c);
+	
+	/* c->x86_power is 8000_0007 edx. Bit 8 is constant TSC */
+	if (c->x86_power & (1<<8))
+		set_bit(X86_FEATURE_CONSTANT_TSC, &c->x86_capability);
 
 	if (c->extended_cpuid_level >= 0x80000008) {
 		c->x86_max_cores = (cpuid_ecx(0x80000008) & 0xff) + 1;
@@ -1231,6 +1235,8 @@ static int show_cpuinfo(struct seq_file 
 		"ttp",  /* thermal trip */
 		"tm",
 		"stc"
+		"?",
+		"constant_tsc",
 	};