ARM: dts: am437x-gp-evm: Don't use read/write wait monitoring

NAND uses wait pin only to indicate device readiness after
a block/page operation. It is not use to extend individual
read/write cycle and so read/write wait pin monitoring must
be disabled for NAND.

This patch also gets rid of the below warning when NAND is
accessed for the first time.

omap_l3_noc 44000000.ocp: L3 application error: target 13 mod:1 (unclearable)

Signed-off-by: Roger Quadros <rogerq@ti.com>
Reviewed-by: Pekon Gupta <pekon@pek-sem.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>