arm64: dts: imx8mm: Add spba1 and spba2 buses

The i.MX8MM reference manual shows there are two spba busses.
SPBA1 handles much of the serial interfaces, and SPBA2 covers much
of the audio.

Add both of them.

Signed-off-by: Adam Ford <aford173@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>