drm/vkms: Compile all tests with CONFIG_DRM_VKMS_KUNIT_TEST

The Kconfig option `CONFIG_DRM_VKMS_KUNIT_TESTS` does not exist. However,
the VKMS format tests use such an option for compilation, meaning that
they are not compiled at all.

Use the Kconfig option `CONFIG_DRM_VKMS_KUNIT_TEST` to compile all VKMS
KUnit tests.

Fixes: 3e897853debd ("drm/vkms: Create KUnit tests for YUV conversions")
Signed-off-by: Maíra Canal <[e-mail]>
Reviewed-by: José Expósito <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Louis Chauvet <[e-mail]>

drivers/gpu/drm/vkms/tests/Makefile

···
 # SPDX-License-Identifier: GPL-2.0-only
 
-obj-$(CONFIG_DRM_VKMS_KUNIT_TEST) += vkms_config_test.o
-obj-$(CONFIG_DRM_VKMS_KUNIT_TESTS) += vkms_format_test.o
+vkms-kunit-tests-y := \
+	vkms_config_test.o \
+	vkms_format_test.o
+
+obj-$(CONFIG_DRM_VKMS_KUNIT_TEST) += vkms-kunit-tests.o