Add Elkhart Lake support

Elkhart Lake has a chipset called Mule Creek Canyon which is quite
compatible with 300 series chipsets. There are a few differences though,
e.g. different encoding for the SPI clock values for read and write in
the FLCOMP register. In addition Elkhart Lake has a new PCI device ID
for the SPI controller which is added, too.

TEST=Read and flash complete flash on Siemens MC EHL1

Change-Id: I711e39a3ec9cd7098389231eaa1cb864d615a475
Signed-off-by: Werner Zeh <werner.zeh@siemens.com>
Reviewed-on: https://review.coreboot.org/c/flashrom/+/60711
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>

programmer.h

@@ -352,6 +352,7 @@ enum ich_chipset {
 	CHIPSET_500_SERIES_TIGER_POINT,
 	CHIPSET_APOLLO_LAKE,
 	CHIPSET_GEMINI_LAKE,
+	CHIPSET_ELKHART_LAKE,
 };
 
 /* ichspi.c */