soc/intel: convert XTAL frequency constant to Kconfig

This converts the constant for the XTAL frequency to a Kconfig option.

Change-Id: I1382dd274eeb9cb748f94c34f5d9a83880624c18
Signed-off-by: Michael Niewöhner <foss@mniewoehner.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/46018
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>

src/soc/intel/skylake/Kconfig

@@ -241,6 +241,9 @@ config SOC_INTEL_COMMON_BLOCK_GSPI_CLOCK_MHZ
 	int
 	default 120
 
+config CPU_XTAL_HZ
+	default 24000000
+
 config DRIVERS_I2C_DESIGNWARE_CLOCK_MHZ
 	int
 	default SOC_INTEL_COMMON_BLOCK_GSPI_CLOCK_MHZ

src/soc/intel/skylake/cpu.c

@@ -169,15 +169,17 @@ static void configure_c_states(void)
  */
 static void enable_pm_timer_emulation(void)
 {
-	/* ACPI PM timer emulation */
 	msr_t msr;
+
+	if (!CONFIG_CPU_XTAL_HZ)
+		return;
+
 	/*
 	 * The derived frequency is calculated as follows:
-	 *    (CTC_FREQ * msr[63:32]) >> 32 = target frequency.
-	 * Back solve the multiplier so the 3.579545MHz ACPI timer
-	 * frequency is used.
+	 * (clock * msr[63:32]) >> 32 = target frequency.
+	 * Back solve the multiplier so the 3.579545MHz ACPI timer frequency is used.
 	 */
-	msr.hi = (3579545ULL << 32) / CTC_FREQ;
+	msr.hi = (3579545ULL << 32) / CONFIG_CPU_XTAL_HZ;
 	/* Set PM1 timer IO port and enable */
 	msr.lo = (EMULATE_DELAY_VALUE << EMULATE_DELAY_OFFSET_VALUE) |
 			EMULATE_PM_TMR_EN | (ACPI_BASE_ADDRESS + PM1_TMR);

src/soc/intel/skylake/include/soc/cpu.h

@@ -25,9 +25,6 @@
 #define C9_POWER	0xc8
 #define C10_POWER	0xc8
 
-/* Common Timer Copy (CTC) frequency - 24MHz. */
-#define CTC_FREQ		24000000
-
 #define C_STATE_LATENCY_MICRO_SECONDS(limit, base) \
 	(((1 << ((base)*5)) * (limit)) / 1000)
 #define C_STATE_LATENCY_FROM_LAT_REG(reg) \