ASoC: Convert pxa directory to module_platform_driver

Factor out some boilerplate code.

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Acked-by: Marek Vasut <marek.vasut@gmail.com>
Acked-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>