arm64: dts: imx8mn: Configure clock rate for audio plls

Configure clock rate for audio plls. audio pll1 is used
as parent clock for clocks that is multiple of 8kHz.
audio pll2 is used as parent clock for clocks that is
multiple of 11kHz.

Signed-off-by: Shengjiu Wang <shengjiu.wang@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>