mtd: nand: Move Macronix specific initialization in nand_macronix.c

Upstream linux commit 3b5206f4be9b65.

Move Macronix specific initialization logic into nand_macronix.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>