soc/intel/apollolake: Add config for cpu base clock frequency

Add config for cpu base clock frequency(Mhz), use and
clean up code.

Change-Id: I724c48c11796aa942295d4f19cc629d4c13647e1
Signed-off-by: Aamir Bohra <aamir.bohra@intel.com>
Reviewed-on: https://review.coreboot.org/20017
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/soc/intel/apollolake/Kconfig

@@ -322,4 +322,8 @@ config IFD_CHIPSET
 	string
 	default "aplk"
 
+config CPU_BCLK_MHZ
+	int
+	default 100
+
 endif