drm/test: add a test suite for GEM objects backed by shmem

This patch introduces an initial KUnit test suite for GEM objects
backed by shmem buffers.
Suggested-by: Javier Martinez Canillas <javierm@redhat.com>
Signed-off-by: Marco Pagani <marpagan@redhat.com>

v5:
- using __drm_kunit_helper_alloc_drm_device() to avoid local struct
v4:
- Add missing MMU dependency for DRM_GEM_SHMEM_HELPER (kernel test robot)
v3:
- Explicitly cast pointers in the helpers
- Removed unused pointer to parent dev in struct fake_dev
- Test entries reordering in Kconfig and Makefile sent as a separate patch
v2:
- Improved description of test cases
- Cleaner error handling using KUnit actions
- Alphabetical order in Kconfig and Makefile
Signed-off-by: Maxime Ripard <mripard@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20231130171417.74162-1-marpagan@redhat.com

drivers/gpu/drm/Kconfig

@@ -74,12 +74,13 @@ config DRM_KUNIT_TEST_HELPERS
 
 config DRM_KUNIT_TEST
 	tristate "KUnit tests for DRM" if !KUNIT_ALL_TESTS
-	depends on DRM && KUNIT
+	depends on DRM && KUNIT && MMU
 	select DRM_BUDDY
 	select DRM_DISPLAY_DP_HELPER
 	select DRM_DISPLAY_HELPER
 	select DRM_EXEC
 	select DRM_EXPORT_FOR_TESTS if m
+	select DRM_GEM_SHMEM_HELPER
 	select DRM_KMS_HELPER
 	select DRM_KUNIT_TEST_HELPERS
 	select DRM_LIB_RANDOM

drivers/gpu/drm/tests/Makefile

@@ -13,6 +13,7 @@ obj-$(CONFIG_DRM_KUNIT_TEST) += \
 	drm_format_helper_test.o \
 	drm_format_test.o \
 	drm_framebuffer_test.o \
+	drm_gem_shmem_test.o \
 	drm_managed_test.o \
 	drm_mm_test.o \
 	drm_modes_test.o \