mainboard/prodrive/hermes: Enable EIST in DeviceTree

Enable EIST option in the devicetree in order to make Windows aware of
using Intel CPU Turbo Technology.

Change-Id: Ied3d7e934fcab2d5d491573245d68d392df5ba34
Signed-off-by: Christian Walter <christian.walter@9elements.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/42777
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Rudolph <siro@das-labor.org>

src/mainboard/prodrive/hermes/variants/baseboard/overridetree.cb

@@ -131,6 +131,9 @@ chip soc/intel/cannonlake
 	# Disable S0ix
 	register "s0ix_enable" = "0"
 
+	# Enable Turbo
+	register "eist_enable" = "1"
+
 	register "common_soc_config" = "{
 		.gspi[0] = {
 			.speed_mhz = 1,