arm64: defconfig: enable bcmbca soc support

Enable CONFIG_ARCH_BCMBCA in defconfig. This config can be used to build
a basic kernel for arm64 based Broadcom Broadband SoC booting to
console.
Signed-off-by: William Zhang <william.zhang@broadcom.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>

arch/arm64/configs/defconfig

@@ -36,6 +36,7 @@ CONFIG_ARCH_ALPINE=y
 CONFIG_ARCH_APPLE=y
 CONFIG_ARCH_BCM2835=y
 CONFIG_ARCH_BCM4908=y
+CONFIG_ARCH_BCMBCA=y
 CONFIG_ARCH_BCM_IPROC=y
 CONFIG_ARCH_BERLIN=y
 CONFIG_ARCH_BRCMSTB=y