soc/intel/skylake: Use real common code for VMX init

Use the common VMX implementation, and set IA32_FEATURE_CONTROL
lock bit per Kconfig *after* SGX is configured (as SGX also sets
bits on the IA32_FEATURE_CONTROL register).

As it is now correctly based on a Kconfig, the `VmxEnable` devicetree
setting vanishes.

Test: build/boot google/[chell,fizz], observe Virtualization enabled
under Windows 10 when VMX enabled and lock bit set.

Change-Id: Iea598cf74ba542a650433719f29cb5c9df700c0f
Signed-off-by: Nico Huber <nico.h@gmx.de>
Signed-off-by: Matt DeVillier <matt.devillier@gmail.com>
Reviewed-on: https://review.coreboot.org/c/29682
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/soc/intel/skylake/chip.h

@@ -465,9 +465,6 @@ struct soc_intel_skylake_config {
 	*/
 	u8 SendVrMbxCmd;
 
-	/* Enable/Disable VMX feature */
-	u8 VmxEnable;
-
 	/*
 	 * PRMRR size setting with three options
 	 * 0x02000000 - 32MiB