mtd: nand: sunxi: add randomizer support

Add support for the randomizer engine available in Allwinner's NFC IP.

Randomization is useful to support modern NAND chips which are sensitive to
repeated patterns. On such NANDs you might experience an unexpectedly high
number of bitflips when you repeat the same pattern all over a given NAND
block.
Randomizing input data mitigate this problem by avoiding such repeated
patterns.

Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>