mtd: spinand: micron: Generalize the OOB layout structure and function names

In order to add new Micron SPI NAND devices, we generalized the OOB
layout structure and function names.

Signed-off-by: Shivamurthy Shastri <sshivamurthy@micron.com>
Acked-by: Jagan Teki <jagan@amarulasolutions.com>