ARM: dts: NSP: Disable PL330 by default, add dma-coherent property

Currently the PL330 is enabled by default. However if left in IDM reset, as is
the case with the Meraki and Synology NSP devices, the system will hang when
probing for the PL330's AMBA peripheral ID. We therefore should be able to
disable it in these cases.

The PL330 is also included among of the list of peripherals put into coherent
mode, so "dma-coherent" has been added here as well.

Fixes: 5fa1026a ("ARM: dts: NSP: Add PL330 support")
Signed-off-by: Matthew Hagan <mnhagan88@gmail.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>