ASoC: imx-wm8962: Remove global variables

Currently the following variables are global:
- card_priv, sample_rate and sample_format

,which is not a good idea as it prevents the usage of multiple
instances.

Make sample_rate and sample_format part of the imx_priv structure
and allocate imx_priv via the standard devm_kzalloc() mechanism
inside the probe function.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Mark Brown <broonie@kernel.org>