mtd: spi-nor: Introduce templates for SPI NOR operations

Clean the op declaration and hide the details of each op. With this it
results a cleanner, easier to read code. No functional change expected.

Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Signed-off-by: Pratyush Yadav <p.yadav@ti.com>
Acked-by: Michael Walle <michael@walle.cc>
Acked-by: Pratyush Yadav <p.yadav@ti.com>
Link: https://lore.kernel.org/r/20220420103427.47867-10-tudor.ambarus@microchip.com