ARM: dts: dm8168-evm: ARM: dts: Disable wait pin monitoring for NAND

The NAND Ready/Busy# line is connected to GPMC_WAIT0 pin and
can't be used for wait state insertion for NAND I/O read/write.
So disable read/write wait monitoring as per Reference Manual's
suggestion [1].

[1] dm816x TRM: SPRUGX8C: 9.2.4.12.2 NAND Device-Ready Pin

Signed-off-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>