drm/sti: Allow build with COMPILE_TEST=y

Allow sti to be built with COMPILE_TEST=y for greater
coverage. Builds fine on x86/x86_64 at least.

Cc: Alain Volmat <alain.volmat@foss.st.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240408170426.9285-8-ville.syrjala@linux.intel.comAcked-by: Alain Volmat <alain.volmat@foss.st.com>

drivers/gpu/drm/sti/Kconfig

 # SPDX-License-Identifier: GPL-2.0-only
 config DRM_STI
 	tristate "DRM Support for STMicroelectronics SoC stiH4xx Series"
-	depends on OF && DRM && ARCH_STI
+	depends on OF && DRM && (ARCH_STI || COMPILE_TEST)
 	select RESET_CONTROLLER
 	select DRM_KMS_HELPER
 	select DRM_GEM_DMA_HELPER