drm/i915: Constify intel_pipe_config_compare()

Now that intel_pipe_config_compare() no longer clobbers the passed
in state we can make both crtc states const. And while at we simplify
the calling convention, and clean up intel_compare_link_m_n() a bit.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190612130801.2085-2-ville.syrjala@linux.intel.com


Reviewed-by: Imre Deak <imre.deak@intel.com>