drm/i915: Add location of the Rcomp resistor to bxt_ddi_phy_info

Use struct bxt_ddi_phy_info to hold information of where the Rcomp
resistor is located, instead of hard coding it in the init sequence.

Note that this moves the enabling of the phy with the Rcomp resistor out
of the power well enable code. That should be safe since
bxt_ddi_phy_init() is called while the power domains lock is held, and
that is the only way that function gets called, so there is no
possibility of a concurrent phy enable caused by a power domain get
call.

v2: Replace comment about lock with lockdep_assert_held()  (Imre)

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/62d209950ad48484564f3e793cf247cf62572a39.1475770848.git-series.ander.conselvan.de.oliveira@intel.com