arm: bcmbca: add bcm4912 SoC support

BCM4912 is a Broadcom B53 based WLAN AP router SoC. It is part of the
BCA (Broadband Carrier Access origin) chipset family so it's added under
ARCH_BCMBCA platform. This initial support includes a bare-bone
implementation and dts with CPU subsystem, memory and ARM PL011 uart.

This SoC is supported in the linux-next git repository so the dts
and dtsi files are copied from linux.

The u-boot image can be loaded from flash or network to the entry
point address in the memory and boot from there to the console.

Signed-off-by: William Zhang <william.zhang@broadcom.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
diff --git a/MAINTAINERS b/MAINTAINERS
index e235a1c..091189b 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -218,6 +218,7 @@
 F:	board/broadcom/bcmbca/
 N:	bcmbca
 N:	bcm[9]?47622
+N:	bcm[9]?4912
 N:	bcm[9]?63138
 N:	bcm[9]?63146
 N:	bcm[9]?63148