Kconfig: nand: Remove redundant dependency on MTD_NAND

Config MTD_NAND_FSL_IFC is already located inside 'if MTD_NAND'
statment, so there's no need to explicitly specify it as a dependency.

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>