ARM: dts: BCM5301x: Add BCM953012ER board

Add support for the Broadcom BCM953012 Enterprise Router reference
board, enable the following peripherals:

- UART0 (UART1 is not populated)
- WPS and restart GPIO buttons
- Ethernet switch w/ only two facing ports
- NAND flash
- SPI-NOR flash

Acked-by: Jon Mason <jon.mason@broadcom.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>