Most of our helpers have relied on being selected so far through
Kconfig, but that creates issues when we have multiple layers of helpers
with some depending on others.

Indeed, select doesn't select a dependency's dependencies, and thus
isn't super intuitive. Depends on however doesn't have that limitation,
so we can just switch all the drivers that were selecting
DRM_DISPLAY_HDCP_HELPER to depend on it.
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Link: https://lore.kernel.org/r/20240327-kms-kconfig-helpers-v3-11-eafee11b84b3@kernel.orgSigned-off-by: Maxime Ripard <mripard@kernel.org>