ASoC: wm5110: Power both channels for differential mono output

On the wm5110 CODEC both the left and right channel must be powered
when an output is being used as a mono output, although no audio is
routed to the right output channel. This patch adds additional DAPM
routes to link the right channel to the left in the case where an output
is marked as mono. Audio must always be brought in on the left channel
for mono operation.

Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@linaro.org>