mtd: brcmnand: Add v7.2 controller support

The 7.2 controller differs in a few area compared to its predecssor (7.1):

- NAND scrambler, which we are not using just yet
- higher ECC levels (up to 120 bits) per 1KB data blocks, also not supported yet
- up to 128B OOB

This patch adds the necessary code to support such a controller
generation and updates the Device Tree binding.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Acked-by: Kamal Dasu <kdasu.kdev@gmail.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>