ARM: dts: mmp2: Add DMA nodes

There is a 16-channel peripheral DMA controller along with two-channel
audio DMA engines.

Link: https://lore.kernel.org/r/20200718205019.184927-7-lkundrak@v3.sk


Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>