arch/x86: Flip option NO_CAR_GLOBAL_MIGRATION

It is easier to track CAR_GLOBAL_MIGRATION which is
the approach to be deprecated with the next release.

This change enforces new policy; POSTCAR_STAGE=y is
not allowed together with CAR_GLOBAL_MIGRATION=y.

Change-Id: I0dbad6a14e68bf566ac0f151dc8ea259e5ae2250
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/34804
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/soc/intel/skylake/Kconfig

@@ -92,7 +92,6 @@ config USE_FSP2_0_DRIVER
 	select PLATFORM_USES_FSP2_0
 	select UDK_2015_BINDING
 	select INTEL_GMA_ADD_VBT if RUN_FSP_GOP
-	select POSTCAR_STAGE
 
 config USE_FSP1_1_DRIVER
 	def_bool y