ASoC: Tegra: Harmony: Support the internal speaker

Add DAPM widget definitions for the internal speaker paths. Currently, this
path is always enabled while playback is active.

Add code to control the speaker amplifier GPIO.

The GPIO is requested during _init, since that's the first time it is
guaranteed that the WM8903 module is loaded, probed, and hence has exported
its GPIO chip.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>