As i915 graphics driver provides the notification via audio component,
not only the currently implemented HSW+ and VLV+ platforms but also
all other PCH-based platforms (e.g. Cougar Point, Panther  Point, etc)
can use this infrastructure.  It'll improve the reliability and the
power consumption significantly, especially once when we implement the
ELD notification via component.  As a preliminary, this patch enables
the usage of audio component for all PCH platforms.

The HDA controller just needs to set AZX_DCAPS_I915_POWERWELL flag
appropriately.  The name of the flag is a bit confusing, but this
actually works even on the chips without the powerwell but accesses
only the other component ops.

In the HDMI/DP codec driver side, we just need to register/unregister
the notifier for such chips.  This can be identified by checking the
audio_component field in the assigned hdac_bus.

One caveat is that PCH for Haswell and Broadwell must not be bound
with i915 audio component, as there are dedicated HD-audio HDMI
controllers on these platforms.  Ditto for Poulsbo and Oaktrail as
they use gma500 graphics, not i915.
Signed-off-by: Takashi Iwai <tiwai@suse.de>