src/cpu/intel: Set get_ia32_fsb function common

Add get_ia32_fsb returns FSB values in MHz of intel's CPUs.
Also add get_ia32_fsb_x3 function. It returns round up 3 * get_ia32_fsb.

Change-Id: I232bf88de7ebba6ac5865db046ce79e9b2f3ed28
Signed-off-by: Elyes HAOUAS <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/30103
Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/include/cpu/intel/fsb.h

@@ -0,0 +1,30 @@
+/*
+ * This file is part of the coreboot project.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; version 2 of the License.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#ifndef CPU_INTEL_FSB_H
+#define CPU_INTEL_FSB_H
+
+/*
+ * This function returns:
+ *	the system bus speed value in MHz
+ *	-1 if FSB is not found
+ *	-2 if the CPU is not supported
+ */
+int get_ia32_fsb(void);
+
+/*
+ * This function returns round up 3 * get_ia32_fsb()
+ */
+int get_ia32_fsb_x3(void);
+
+#endif /* CPU_INTEL_FSB_H */