CHV has 2 display phys.  First phy (IOSF offset 0x1A) has two channels,
and second phy (IOSF offset 0x12) has single channel.  The first phy is
used for port B and port C, while second phy is only for port D.

v2: Move the pipe to determine which phy to select for
vlv_dpio_read/vlv_dpio_write to another patch. (Daniel)
v3: Rebase the code based on rework on how to calculate DPIO offset.
Signed-off-by: NChon Ming Lee <chon.ming.lee@intel.com>
Reviewed-by: NImre Deak <imre.deak@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>