drm/dp: switch drm_dp_vsc_sdp_log() to struct drm_printer

Use the existing drm printer infrastructure instead of local macros.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Luca Coelho <luciano.coelho@intel.com>
Acked-by: Maxime Ripard <mripard@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/cdf8faf272d345de215feb6ececba384ecaecdb4.1705410327.git.jani.nikula@intel.com