MIPS: BMIPS: Add BCM7435 dtsi

Add the bare minimum required to boot a BCM7435-based system:

- BMIPS5200 CPU nodes
- Level 1 and 2 interrupt controllers
- UARTs
- EHCI/OHCI controllers

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Cc: linux-mips@linux-mips.org
Cc: blogic@openwrt.org
Cc: cernekee@chromium.org
Cc: Steven.Hill@imgtec.com
Patchwork: https://patchwork.linux-mips.org/patch/9971/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>