ASoC: pxa: Fix module autoload for platform drivers

commit e5b7d71a upstream.

These platform drivers are lacking MODULE_ALIAS so module autoloading
doesn't work. Tested on corgi and poodle with kernel 4.4.

Signed-off-by: Andrea Adami <andrea.adami@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>