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/Kconfig

@@ -29,6 +29,7 @@ config CPU_SPECIFIC_OPTIONS
 	select BOOTBLOCK_SAVE_BIST_AND_TIMESTAMP
 	select C_ENVIRONMENT_BOOTBLOCK
 	select HAVE_HARD_RESET
+	select HAVE_MONOTONIC_TIMER
 	select NO_MMCONF_SUPPORT
 	select REG_SCRIPT
 	select RELOCATABLE_RAMSTAGE