ALSA: hda: add mute LED support for HP EliteBook 840 G4

ALSA: hda: add mute LED support for HP EliteBook 840 G4

BugLink: https://bugs.launchpad.net/bugs/1837257
commit 40906ebe3af6a48457151b3c6726b480f6a6cb13 upstream.

Tested with 4.19.9.

v2: Changed from CXT_FIXUP_MUTE_LED_GPIO to CXT_FIXUP_HP_DOCK because
    that's what the existing fixups for EliteBooks use.

Signed-off-by: Mantas Mikulėnas <grawity@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>