ASoC: wm5110: Add special DRE on/off handling for the headphone path

For the best performance the headphone path enable/disable must be
handled specially for the situations of DRE on and DRE off.

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