ARM: dts: imx6qdl-kontron-samx6i: fix node names

Rename the nodes according to the schema. In particular, rename the bit
bang I2C controller to "i2c-N" and the mux nodes of the audmux to
"mux-*". While at it, fix the typo "adu", which should have been "aud".

Signed-off-by: Michael Walle <mwalle@kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>