ARM: dts: add dts files for bcmbca soc 47622

Add dts for ARMv7 based broadband SoC BCM47622. bcm47622.dtsi is the
SoC description dts header and bcm947622.dts is a simple dts file for
Broadcom BCM947622 Reference board that only enable the UART port.

Signed-off-by: William Zhang <william.zhang@broadcom.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>