ARM: bcm: Select ARM_AMBA for ARCH_BRCMSTB

BCM7211 uses a PL011 UART and is supported using ARCH_BRCMSTB, make sure
that we can enable that driver by selecting ARM_AMBA.
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>

arch/arm/mach-bcm/Kconfig

@@ -211,6 +211,7 @@ config ARCH_BRCMSTB
 	bool "Broadcom BCM7XXX based boards"
 	depends on ARCH_MULTI_V7
 	select ARCH_HAS_RESET_CONTROLLER
+	select ARM_AMBA
 	select ARM_GIC
 	select ARM_ERRATA_798181 if SMP
 	select HAVE_ARM_ARCH_TIMER