treewide: Replace CONFIG(ARCH_xx) tests

Once we support building stages for different architectures,
such CONFIG(ARCH_xx) tests do not evaluate correctly anymore.

Change-Id: I599995b3ed5c4dfd578c87067fe8bfc8c75b9d43
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/42183
Reviewed-by: Raul Rangel <rrangel@chromium.org>
Reviewed-by: Furquan Shaikh <furquan@google.com>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/include/cbmem.h

@@ -145,7 +145,7 @@ void cbmem_add_records_to_cbtable(struct lb_header *header);
  * and CBMEM_CONSOLE. Sometimes it is necessary to have cbmem_top()
  * value stored in nvram to enable early recovery on S3 path.
  */
-#if CONFIG(ARCH_X86)
+#if ENV_X86
 void backup_top_of_low_cacheable(uintptr_t ramtop);
 uintptr_t restore_top_of_low_cacheable(void);
 #endif