drm/mst: remove mgr parameter and debug logging from drm_dp_get_vc_payload_bw()

The struct drm_dp_mst_topology_mgr *mgr parameter is only used for debug
logging in case the passed in link rate or lane count are zero. There's
no further error checking as such, and the function returns 0.

There should be no case where the parameters are zero. The returned
value is generally used as a divisor, and if we were hitting this, we'd
be seeing division by zero.

Just remove the debug logging altogether, along with the mgr parameter,
so that the function can be used in non-MST contexts without the
topology manager.

v2: Also remove drm_dp_mst_helper_tests_init as unnecessary (Imre)

Cc: Imre Deak <imre.deak@intel.com>
Cc: Lyude Paul <lyude@redhat.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Acked-by: Maxime Ripard <mripard@kernel.org>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/72d77e7a7fe69c784e9df048b7e6f250fd7599e4.1735912293.git.jani.nikula@intel.com