cpu init: support for no_turbo kernel argument

arch/x86/kernel/cpu.c

@@ -117,6 +117,7 @@ extern char page_fault[], general_protection_exception[];
 extern char debug_exception[], int3_exception[];
 
 uint64_t boot_pat_state = 0;
+int no_turbo = 0; /* May be updated by early parsing of kargs */
 
 static void init_idt(void)
 {
@@ -292,6 +293,7 @@ void init_pstate_and_turbo(void)
 	 * When set to 1: disengages IDA
 	 * When set to 0: enables IDA
 	 */
+	if (!no_turbo) {
 		if (eax & (1 << 1)) {
 			uint64_t turbo_value;
 
@@ -312,6 +314,7 @@ void init_pstate_and_turbo(void)
 		else {
 			value = value << 8;
 		}
+	}
 
 	wrmsr(MSR_IA32_PERF_CTL, value);