drm/i915: Explicitly map broxton DPIO power wells to phys

The mapping from the BXT_DPIO_CMN_* power wells to their respective phys
required a detour implemented in the bxt_power_well_to_phy() function.
Instead, embed that information directly into the power_well struct, by
resurrecting the data field.

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/7fe97582fa08c7340ce6a3b6b0ea3e72a73182d7.1475770848.git-series.ander.conselvan.de.oliveira@intel.com