intelhdmi - dont power off HDA link

For codecs without EPSS support (G45/IbexPeak), the hotplug event will
be lost if the HDA is powered off during the time. After that the pin
presence detection verb returns inaccurate info.

So always power-on HDA link for !EPSS codecs.

KarL offers the fact and Takashi recommends to flag hda_bus. Thanks!

Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>