arch/x86: Simplify <arch/early_variables.h>

This enables the use of .bss section for ENV_BOOTBLOCK
and ENV_VERSTAGE even with CAR_GLOBAL_MIGRATION=y.

In practice, boards with CAR_GLOBAL_MIGRATION=y currently
build with romcc-bootblock so they will not be using .bss.

Change-Id: Ie9dc14f3e528d3e4f48304f4d7de50df448a8af6
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/35016
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>

src/lib/program.ld

@@ -125,7 +125,7 @@
 }
 #endif
 
-#if ENV_STAGE_HAS_BSS_SECTION
+#if ENV_STAGE_HAS_BSS_SECTION && !ENV_CACHE_AS_RAM
 .bss . : {
 	. = ALIGN(ARCH_POINTER_ALIGN_SIZE);
 	_bss = .;