drm/imx/dcss: Allow build with COMPILE_TEST=y

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

Cc: Laurentiu Palcu <laurentiu.palcu@oss.nxp.com>
Cc: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241003111851.10453-8-ville.syrjala@linux.intel.com


Reviewed-by: Laurentiu Palcu <laurentiu.palcu@oss.nxp.com>