drm/display: Make DisplayPort AUX Chardev Kconfig name consistent

While most display helpers Kconfig symbols have the DRM_DISPLAY prefix,
the DisplayPort-AUX chardev interface uses DRM_DP_AUX_CHARDEV.

Since the number of users is limited and it's a selected symbol, we can
easily rename it to make it consistent.

Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://lore.kernel.org/r/20240327-kms-kconfig-helpers-v3-3-eafee11b84b3@kernel.org


Signed-off-by: Maxime Ripard <mripard@kernel.org>