purism/librem_skl: Enable VMX and Intel SpeedStep in devicetree

Although VmxEnable is currently ignored by FSP, a forthcoming patch
explicitly enables it in coreboot, so set it in anticipation of that.

Enable Intel SpeedStep to ensure the ACPI tables are generated for
the C-states/P-states which are required for the xen-acpi-processor
module to be loaded. Without it, the Qubes 4.0-rc4 installer will
complain at boot about modules that could not be loaded.

Change-Id: I968ef36ec9382a10db13d96fd3a5c0fc904db387
Signed-off-by: Youness Alaoui <youness.alaoui@puri.sm>
Signed-off-by: Matt DeVillier <matt.devillier@gmail.com>
Reviewed-on: https://review.coreboot.org/23684
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/src/mainboard/purism/librem_skl/variants/librem13v2/devicetree.cb b/src/mainboard/purism/librem_skl/variants/librem13v2/devicetree.cb
index b85ac3e..84932b2 100644
--- a/src/mainboard/purism/librem_skl/variants/librem13v2/devicetree.cb
+++ b/src/mainboard/purism/librem_skl/variants/librem13v2/devicetree.cb
@@ -7,6 +7,9 @@
 	register "deep_s5_enable_dc" = "0"
 	register "deep_sx_config" = "DSX_EN_LAN_WAKE_PIN"
 
+	register "eist_enable" = "1"
+	register "VmxEnable" = "1"
+
 	# GPE configuration
 	# Note that GPE events called out in ASL code rely on this
 	# route. i.e. If this route changes then the affected GPE