drm/i915: Make intel_dp_source_supports_hbr2() take an intel_dp pointer

The function name implies it should get intel_dp, and it mostly used
where there is an intel_dp in the context.

Signed-off-by: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Reviewed-by: Sivakumar Thulasimani <sivakumar.thulasimani@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1445594525-7174-8-git-send-email-ander.conselvan.de.oliveira@intel.com