ALSA: hda - Fix powermap for external mics on IDT codecs

This patch fixes a regression of the external mic not working on
HP Probook 4520s.

Signed-off-by: David Henningsson <david.henningsson@canonical.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
ALSA: hda - Update documentation

Signed-off-by: Takashi Iwai <tiwai@suse.de>