On Skylake and onwards, the HD-audio controller driver needs to bind
with i915 for having the control of power well audio domain before
actually probing the codec.  This leads to the load of i915 driver
from the audio driver side.  But, there are systems that have no Intel
graphics but Nvidia or AMD GPU, although they still use HD-audio bus
for the onboard audio codecs.  On these, loading the i915 driver is
nothing but a useless memory and CPU consumption.

A simple way to avoid it is just to look for the Intel graphics PCI
entry beforehand, and try to bind with i915 only when such an entry is
found.  Currently, it assumes the PCI display class.  If another class
appears, this needs to be extended (although it's very unlikely).
Signed-off-by: Takashi Iwai <tiwai@suse.de>