ARM: dts: rockchip: add SPI flash node for rk3288-veyron

This is a standard binding for describing SPI flash that can be
identified by reading their JEDEC ID. Let's use it.

Tested on Veyron Jaq.

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>