ALSA: hdac: add snd_hdac_refresh_widget_sysfs()

Some codecs like Intel HDMI by default do not show up all the pins, they
have to be manually enabled, so we need to refresh the codec widgets and
then recreate the sysfs tree. So add new API snd_hdac_refresh_widget_sysfs()
to do this. It should be be used by codec driver after sending magic verbs
to codec

Signed-off-by: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>