Revert "mtd: spi-nor: Add support for statefull Octal IO mode"

This reverts commit a8648756.

Octal IO mode will be added in a future patch that is based on a more
recent patchset posted upstream. It uses Octal DTR mode without having
to maintain the state and has a different way of activating it.

Signed-off-by: Pratyush Yadav <p.yadav@ti.com>