security/intel/txt/romstage: add missing arch/cpu.h include

Including arch/cpu.h is needed to have the declaration for
cpu_get_feature_flags_ecx.

Signed-off-by: Felix Held <felix-coreboot@felixheld.de>
Change-Id: I091c82f5a55ee9aa84a255c75c7721eff989344d
Reviewed-on: https://review.coreboot.org/c/coreboot/+/57726
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Raul Rangel <rrangel@chromium.org>

src/security/intel/txt/romstage.c

@@ -1,5 +1,6 @@
 /* SPDX-License-Identifier: GPL-2.0-only */
 
+#include <arch/cpu.h>
 #include <arch/mmio.h>
 #include <cf9_reset.h>
 #include <console/console.h>