mtd: nand: Move Toshiba specific init/detection logic in nand_toshiba.c

Upstream linux commit 9b2d61f80b060c.

Move Toshiba specific initialization and detection logic into
nand_toshiba.c. This is part of the "separate vendor specific code from
core" cleanup process.

Signed-off-by: Michael Trimarchi <michael@amarulasolutions.com>
Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>