drm/selftest: plane_helper: Put test structures in static storage

Clang warns on certain 32-bit architectures:

  drivers/gpu/drm/selftests/test-drm_plane_helper.c:76:5: warning: stack frame size (1064) exceeds limit (1024) in 'igt_check_plane_state' [-Wframe-larger-than]
  int igt_check_plane_state(void *ignored)
      ^
  1 warning generated.

The structures in igt_check_plane_state() total 1008 bytes, so any small
amount of inlining will cause the stack frame to exceed the 32-bit limit
of 1024, triggering the warning.

Move these structures to static storage, which dramatically reduces the
amount of stack space in igt_check_plane_state(). There is no testing
impact, as igt_check_plane_state() is only called once in the driver.

Fixes: 943e6a8 ("mock a drm_plane in igt_check_plane_state to make the test more robust")
Link: ClangBuiltLinux#1600
Reported-by: kernel test robot <lkp@intel.com>
Suggested-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20220302235909.784935-1-nathan@kernel.org

Author: nathanchance

drivers/gpu/drm/selftests/test-drm_plane_helper.c

@@ -77,7 +77,7 @@ int igt_check_plane_state(void *ignored)
 {
 	int ret;
 
-	const struct drm_crtc_state crtc_state = {
+	static const struct drm_crtc_state crtc_state = {
 		.crtc = ZERO_SIZE_PTR,
 		.enable = true,
 		.active = true,
@@ -87,14 +87,14 @@ int igt_check_plane_state(void *ignored)
 				DRM_MODE_FLAG_NHSYNC | DRM_MODE_FLAG_NVSYNC)
 		},
 	};
-	struct drm_plane plane = {
+	static struct drm_plane plane = {
 		.dev = NULL
 	};
-	struct drm_framebuffer fb = {
+	static struct drm_framebuffer fb = {
 		.width = 2048,
 		.height = 2048
 	};
-	struct drm_plane_state plane_state = {
+	static struct drm_plane_state plane_state = {
 		.plane = &plane,
 		.crtc = ZERO_SIZE_PTR,
 		.fb = &fb,