TI DaVinci: DM355 Leopard: Fix compilation warning

We get a compliation warning when we enable the NAND driver
for DM355 leopard. The waring we get is that we have
an implicit declaration of davinci_nand_init.

It is fixed by including the asm/arch/nand_defs.h header file

Signed-off-by: Sandeep Paulraj <s-paulraj@ti.com>