ASoC: fsl: micfil: Use dual license micfil code

We need this in order to easily reuse register definitions
and some functions with Sound Open Firmware driver.

According to Documentation/process/license-rules.rst:
    "Dual BSD/GPL"	The module is dual licensed under a GPL v2
			variant or BSD license choice. The exact
			variant of the BSD license can only be
			determined via the license information
			in the corresponding source files.

so use "Dual BSD/GPL" for license string.

Signed-off-by: Shengjiu Wang <shengjiu.wang@nxp.com>
Signed-off-by: Daniel Baluta <daniel.baluta@nxp.com>
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>
Link: https://lore.kernel.org/r/20230803072638.640789-1-daniel.baluta@oss.nxp.com
Signed-off-by: Mark Brown <broonie@kernel.org>