staging: mt7621-dts: get rid of nodes with no in-tree driver

Nodes for 'i2s' and 'nand' have no driver present inside the linux tree.
The normal approach for a dts file to be mainlined is start with those stuff
which is already mainlined and get rid of the other stuff. If needed it will
be properly added afterwards together with the suitable device driver. Hence,
remove both nodes from the device tree include file.

Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Link: https://lore.kernel.org/r/20211018170206.11959-1-sergio.paracuellos@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>