mtd: nand: Rename nand.h into rawnand.h

mtd: nand: Rename nand.h into rawnand.h

This header was renamed to rawnand.h in Linux.

The following is the corresponding commit in Linux.

  commit d4092d76a4a4e57b65910899948a83cc8646c5a5
  Author: Boris Brezillon <boris.brezillon@free-electrons.com>
  Date:   Fri Aug 4 17:29:10 2017 +0200

      mtd: nand: Rename nand.h into rawnand.h

      We are planning to share more code between different NAND based
      devices (SPI NAND, OneNAND and raw NANDs), but before doing that
      we need to move the existing include/linux/mtd/nand.h file into
      include/linux/mtd/rawnand.h so we can later create a nand.h header
      containing all common structure and function prototypes.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>