drm/i915: Address broxton phy registers based on phy and channel number

The port registers related to the phys in broxton map to different
channels and specific phys. Make that mapping explicit.

v2: Pass enum dpio_phy to macros instead of mmio base. (Imre)

v3: Fix typo in macros. (Imre)

v4: Also change variables from u32 to enum dpio_phy. (Imre)
    Remove leftovers from previous version. (Imre)

v5: Actually git add the changes.

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/1476863940-6019-1-git-send-email-ander.conselvan.de.oliveira@intel.com