Currently we disallow the runtime PM of the HD-audio controller if
it's bound with HDMI/DP on Nvidia / AMD unless it's for dGPU.  This is
for keeping the link up to get the proper notification for ELD
hotplug.

As explained in the commit 37a3a98e ("ALSA: hda - Enable runtime
PM only for discrete GPU"), this keep-power-up behavior is rather a
stop-gap solution until the ELD notification via audio component.
And now we finally got the audio component for these graphics drivers
via commit ade49db3 ("ALSA: hda/hdmi - Allow audio component for
AMD/ATI and Nvidia HDMI"), so it's time to change.

This patch makes HD-audio controller again runtime-suspendable when
the device gets bound with audio component in HDMI codec driver.  For
making it easier to access from the codec driver, move the flag into
the common hda_bus object instead of hda_intel flag.  Also rename it
to keep_power, to indicate the actual meaning.
Signed-off-by: Takashi Iwai <tiwai@suse.de>