This patch adds the mute LED control for HP Spectre x360 Kabylake
model.  The mute LED is controlled via VREF bits on NID 0x1b, so we
need a new fixup function.

Note that this doesn't fix the other issues like the missing speaker
output on the machine.  They will be addressed by later patches.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=189331Signed-off-by: Tom Briden <tom@decompile.me.uk>
Signed-off-by: Takashi Iwai <tiwai@suse.de>