CHROMIUM: Add #line to arm_mpu.c

Work around coreboot GCC preprocessor bug.

BUG=b:272518464
TEST=BOARD=craask ; zmake build --coverage $BOARD &&
./util/find_non_exec_lines.py build/zephyr/$BOARD/output/zephyr.info
GWSQ_IGNORES=asemjonovs

Change-Id: Ib9c19bc8ba2328dcc37886a0a0350a77dea7fb8f
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/zephyr/+/5692002
Tested-by: Jeremy Bettis <jbettis@chromium.org>
Reviewed-by: Tomasz Michalec <tmichalec@google.com>
Commit-Queue: Jeremy Bettis <jbettis@chromium.org>

arch/arm/core/mpu/arm_mpu.c

@@ -4,6 +4,12 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+/*
+ * TODO(b/272518464): Work around coreboot GCC preprocessor bug.
+ * #line marks the *next* line, so it is off by one.
+ */
+#line 12
+
 #include <zephyr/device.h>
 #include <zephyr/init.h>
 #include <zephyr/kernel.h>