mtd: nand: davinci: fix the binding documentation

Since the aemif driver conversion to DT along with
its movement to drivers/ folder is not yet done,
fix NAND binding documentation to have NAND specific
DT details only.

Signed-off-by: Kumar, Anil <anilkumar.v@ti.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>