northbridge/intel/gm45: Use TSC for ramstage timer per default

This is a step towards isolating the timer drivers.

Change-Id: I4c9349054be0cf520cd4407be9fb393b664223a4
Signed-off-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Reviewed-on: https://review.coreboot.org/13922
Tested-by: build bot (Jenkins)
Reviewed-by: Martin Roth <martinroth@google.com>

src/northbridge/intel/gm45/Kconfig

@@ -26,6 +26,7 @@ config NORTHBRIDGE_SPECIFIC_OPTIONS # dummy
 	select VGA
 	select INTEL_EDID
 	select INTEL_GMA_ACPI
+	select UDELAY_TSC
 
 config CBFS_SIZE
 	hex