Merge tag 'arc-last-minute-for-2019.04' of git://git.denx.de/u-boot-arc

This is last minute change which fixes problems in runtime on
AXS10x board caused by some changes in NAND framework and
tiny documentation improvement.

Anyways NAND flash storage was never really used on the board for various
reasons and now we decided to drop it for good.

Note this change only touches 1 ARC board so that should be safe for others.
As usual - build tested in TravisCI, see
https://travis-ci.org/abrodkin/u-boot/builds/512041342