mtd: nand: davinci: add header file for driver definitions

The definitions inside emif_defs.h concern davinci nand driver and
should be in it's header. So create header file for davinci nand
driver and move definitions from emif_defs.h and nand_defs.h to it.

Acked-by: Vitaly Andrianov <vitalya@ti.com>
Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@ti.com>
[trini: Fixup more davinci breakage]
Signed-off-by: Tom Rini <trini@ti.com>