reset: imx8mp-audiomix: Switch to using regmap API

reset: imx8mp-audiomix: Switch to using regmap API

Switch to using the regmap API to allow performing register operations
under the same lock. This is needed for cases such as i.MX8ULP's SIM LPAV
where clock gating, reset control and MUX-ing is performed via the same
register (i.e. SYSCTRL0) and different subsystem APIs.

Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Signed-off-by: Laurentiu Mihalcea <laurentiu.mihalcea@nxp.com>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>