drm/i915/bdw: pretend we have LPT LP on Broadwell

The platforms we currently have all have LPT LP on them. As such, we
have no way to identify the new WPT PCH that will ship with Broadwell.

NOTE: For all purposes relevant to the driver that this point, LPT and
WPT are equivalent. Therefore there should be no need to actually change
this for some time.

v2: Don't assign dev_priv->num_pch_pll any more.

v3: Rebase on top of the PCH detection changes for virtualized
enviroments.

v4: Wrote commit message

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com> (v1)
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch> (v3)
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>