ARM: dts: NSP: Add DT files for Meraki MX64 series

MX64 & MX64W Hardware info:
  - CPU: Broadcom BCM58625 Cortex A9 @ 1200Mhz
  - RAM: 2 GB (4 x 4Gb SK Hynix H5TC4G83CFR)
  - Storage: 1 GB (Micron MT29F8G08ABACA)
  - Networking: BCM58625 internal switch (5x 1GbE ports)
  - USB: 1x USB2.0
  - Serial: Internal header
  - WLAN(MX64W only): 2x Broadcom BCM43520KMLG on the PCI bus

This patch adds the Meraki MX64 series-specific bindings. Since some
devices make use of the older A0 SoC, changes need to be made to
accommodate this case, including removal of coherency options and
modification to the secondary-boot-reg.

Signed-off-by: Matthew Hagan <mnhagan88@gmail.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>