ARM: dts: dra72-evm: Add NAND support

DRA72-evm has a 256MB 16-bit wide NAND chip. Add
pinmux and NAND node.

The NAND chips 'Chip select' and 'Write protect' can be
controlled using DIP Switch SW5. To use NAND,
the switch must be configured like so:

SW5.1 (NAND_SELn) = ON (LOW)
SW5.9 (GPMC_WPN) = OFF (HIGH)

Signed-off-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Tested-by: Nishanth Menon <nm@ti.com>
Acked-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>