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/lib/imd_cbmem.c

@@ -41,7 +41,7 @@
  */
 #define CAN_USE_GLOBALS \
 	(!CONFIG(ARCH_X86) || ENV_RAMSTAGE || ENV_POSTCAR || \
-	 CONFIG(NO_CAR_GLOBAL_MIGRATION))
+	 !CONFIG(CAR_GLOBAL_MIGRATION))
 
 static inline struct imd *cbmem_get_imd(void)
 {