MIPS: BMIPS: Add support for Broadcom BCM97435SVMB

Add a DTS file and Kconfig entry for the BCM97435SVMB evaluation board
using bcm7435.dtsi as an example.

The current code needs some tweaking to allow us to use the
dual-threaded dual BMIPS5200 CPUs, so for now we limit ourselves to
allowing just a single CPU to be booted.

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/9972/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>