mtd: remove tmio_nand driver

With the TMIO MFD drivers gone, the NAND support is also
obsolete and can be removed.

Cc: Miquel Raynal <miquel.raynal@bootlin.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: Vignesh Raghavendra <vigneshr@ti.com>
Cc: linux-mtd@lists.infradead.org
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>