mtd: nand: provide several helpers to do common NAND operations

mtd: nand: provide several helpers to do common NAND operations

Linux commit 97d90da8a88 ("mtd: nand: provide several helpers
to do common NAND operations")

This is part of the process of removing direct calls to ->cmdfunc()
outside of the core in order to introduce a better interface to execute
NAND operations.

Here we provide several helpers and make use of them to remove all
direct calls to ->cmdfunc(). This way, we can easily modify those
helpers to make use of the new ->exec_op() interface when available.

Signed-off-by: Boris Brezillon <[email protected]>
[[email protected]: rebased and fixed some conflicts]
Signed-off-by: Miquel Raynal <[email protected]>
Acked-by: Masahiro Yamada <[email protected]>
[Philippe Reynes: adapt code to u-boot and only keep new function]

Signed-off-by: Philippe Reynes <[email protected]>