haswell: Properly Guard Engergy Policy by CPUID

The IA32_ENERGY_PERFORMANCE_BIAS MSR can only be read or written
to if the CPU supports it. The support is indicated by ECX[3] for
cpuid(6). Without this guard, some Haswell parts would GP# fault
in this routine.

No more GP# while running on haswell CRBs.

Change-Id: If41e1e133e5faebb3ed578cba60743ce7e1c196f
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/2639
Tested-by: build bot (Jenkins)
Reviewed-by: Martin Roth <martin.roth@se-eng.com>

src/cpu/intel/haswell/haswell_init.c

@@ -404,6 +404,12 @@ static void set_max_ratio(void)
 static void set_energy_perf_bias(u8 policy)
 {
 	msr_t msr;
+	int ecx;
+
+	/* Determine if energy efficient policy is supported. */
+	ecx = cpuid_ecx(0x6);
+	if (!(ecx & (1 << 3)))
+		return;
 
 	/* Energy Policy is bits 3:0 */
 	msr = rdmsr(IA32_ENERGY_PERFORMANCE_BIAS);