drm/i915: Move broxton phy code to intel_dpio_phy.c

The phy in broxton is also a dpio phy, similar to cherryview but with
programming through MMIO. So move the code together with the other
similar phys.

Signed-off-by: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/d611de6d256593cf904172db7ff27f164480c228.1475770848.git-series.ander.conselvan.de.oliveira@intel.com