nb/intel/sandybridge: Rewrite get_FRQ

The code is just clamping the frequency index to a valid range. Do it
with a helper function. Also, add a CPUID check, as Sandy Bridge will
eventually use this code.

Change-Id: I4c7aa5f7615c6edb1ab62fb004abb126df9d284b
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/39787
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>

src/commonlib/include/commonlib/clamp.h

@@ -0,0 +1,22 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#ifndef COMMONLIB_CLAMP_H
+#define COMMONLIB_CLAMP_H
+
+#include <stdint.h>
+
+/*
+ * Clamp a value, so that it is between a lower and an upper bound.
+ */
+static inline u32 clamp_u32(const u32 min, const u32 val, const u32 max)
+{
+	if (val > max)
+		return max;
+
+	if (val < min)
+		return min;
+
+	return val;
+}
+
+#endif /* COMMONLIB_CLAMP_H */