ARM: dts: vexpress: set the right partition type for NOR flash

We should set up the partitions in the right way so we will find out
what is in the flash.

The ARM Firmware Suite now has its own compatible and proper device
tree bindings to trigger discovery of the flash contents, and Linux
supports handling the new type of AFS partitions.

Based on commit 7f8e78ca ("arm64: dts: juno: set the right partition
type for NOR flash")

Cc: Liviu Dudau <liviu.dudau@arm.com>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>