soc/intel/quark: Add monotonic timer support

Add the Kconfig value HAVE_MONOTONIC_TIMER and the routine to read the
TSC for the monotonic timer.  Simplify the routine to get the TSC
frequency.

TEST=Build and run on Galileo Gen2

Change-Id: I806fb864b01e39277bf2d6276254b0543930c2f6
Signed-off-by: Lee Leahy <leroy.p.leahy@intel.com>
Reviewed-on: https://review.coreboot.org/18002
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Martin Roth <martinroth@google.com>

src/soc/intel/quark/tsc_freq.c

@@ -17,20 +17,18 @@
 #include <stdint.h>
 #include <cpu/x86/msr.h>
 #include <cpu/x86/tsc.h>
-
-static unsigned long bus_freq_khz(void)
-{
-	/* CPU freq = 400 MHz */
-	return 400 * 1000;
-}
+#include <timer.h>
 
 unsigned long tsc_freq_mhz(void)
 {
-	/* assume ratio=1 */
-	unsigned bclk_khz = bus_freq_khz();
-
-	if (!bclk_khz)
-		return 0;
-
-	return (bclk_khz * 1) / 1000;
+	/* CPU freq = 400 MHz */
+	return 400;
+}
+
+void timer_monotonic_get(struct mono_time *mt)
+{
+	uint64_t tsc_value;
+
+	tsc_value = rdtscll();
+	mt->microseconds = tsc_value / tsc_freq_mhz();
 }