reset: imx8mp-audiomix: Prepare the code for more reset bits

reset: imx8mp-audiomix: Prepare the code for more reset bits

Current code supports EARC PHY Software Reset and EARC Software Reset
but it is not easily extensible to more reset bits.

So, refactor the code in order to easily allow more reset bits in the
future.

Reviewed-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Signed-off-by: Daniel Baluta <daniel.baluta@nxp.com>
Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>
Link: https://lore.kernel.org/r/20250311085812.1296243-6-daniel.baluta@nxp.com
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>