bcm96753ref: add initial support

This add the initial support of the broadcom reference
board bcm96753ref with a bcm6753 SoC.

This board has 1 GB of RAM, 256 MB of flash (nand),
2 USB port, 1 UART, and 4 ethernet ports.

Signed-off-by: Philippe Reynes <philippe.reynes@softathome.com>
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 6ce683a..8c7f317 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -2213,6 +2213,7 @@
 source "board/armltd/vexpress64/Kconfig"
 source "board/cortina/presidio-asic/Kconfig"
 source "board/broadcom/bcm963158/Kconfig"
+source "board/broadcom/bcm96753ref/Kconfig"
 source "board/broadcom/bcm968360bg/Kconfig"
 source "board/broadcom/bcm968580xref/Kconfig"
 source "board/broadcom/bcmns3/Kconfig"