ARC: AXS10x: drop NAND support

On AXS10x boards we have non-standard NAND controller
which was never really used a lot as there're other much more
convenient [as they are standard & removable] persistent media
like SD-card and USB mass storage.

Moreover after recent changes we face with some NAND controller
runtime issues. So instead of keeping support of yet another
non-standard peripheral we're dropping its support for good.

Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>