ALSA: hda - WAKEEN feature enabling for runtime pm

With runtime power save feature enabled, Headphone hotplug
event will not be detected while controller/codec in D3. HDA has
feature WAKEEN to let codec wake up system if controller is in D3 or
system in S3.(HDA Spec 4.5.9.2/3). Codec can send out INT or wake up
controller depending on whether CIE or GIE enabled.(Figure 4, Interupt
structure).

The controller must be in RESET mode after enter runtime-suspend, otherwise
it will not be waken up even if codec send out wake-up event. And STATESTS
will be cleared after controller brought out of RESET mode.

This patch only enable WAKEEN for runtime-suspend(Controller D3) mode,
not for system S3 mode. with tool "evtest", Headphone hotplug events
could be cought and reported successfully.

[fixed an unused variable warning by tiwai]

Signed-off-by: Wang Xingchao <xingchao.wang@linux.intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>