drm/i915: Change the placement of some static functions in intel_dp.c

These static helper functions are required to be used during
fallback link rate implemnetation so they need to be placed at the top
of the file.

v3:
* Add cleanup to other patch (Mika Kahola)
v2:
* Dont move around functions declared in intel_drv.h (Rodrigo Vivi)

Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@intel.com>
Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
Reviewed-by: Mika Kahola <mika.kahola@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1477524358-16563-4-git-send-email-manasi.d.navare@intel.com