mtd: brcmnand: Add support for v6.2 controllers

mtd: brcmnand: Add support for v6.2 controllers

Document and match the brcm,brcmnand-v6.2 compatible string, the controller has
a register layout identical to the v6.0 version and supports prefetch. Update the
command shift logic to account for v6.2 controller which are the first ones to
use a shift of 0 (6.1 used a shift of 24).

Signed-off-by: Kamal Dasu <[email protected]>
Signed-off-by: Florian Fainelli <[email protected]>
Acked-by: Rob Herring <[email protected]>
Acked-by: Brian Norris <[email protected]>
Signed-off-by: Boris Brezillon <[email protected]>