mtd: spinand: Add support for randomizer

mtd: spinand: Add support for randomizer

This patch adds support for the randomizer feature.

It introduces a 'set_randomizer' callback in 'struct spinand_info' and
'struct spinand_device'.

If a driver implements this callback, the core will invoke it during
device initialization (spinand_init) to enable or disable the randomizer
feature based on the device tree configuration.

Signed-off-by: Cheng Ming Lin <chengminglin@mxic.com.tw>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>