drm/i915: Reduce diff to Linux 3.17 in i915/intel_dp.c

drm/i915: Reduce diff to Linux 3.17 in i915/intel_dp.c

Replaces intel_dp_aux_native_* calls by the corresponding drm_dp_dpcd_*
calls used in the Linux 3.17 code, and removes the intel_dp_aux_native_*
functions.

intel_dp_aux_native_read_retry() became intel_dp_dpcd_read_wake().
One operator precedence typo which wasn't synced from Linux 3.17 code
yet, and some whitespace diff fixes