bus: brcmstb_gisb: Rework dependencies

Do not have the machine Kconfig entry point need to select
BRCMSTB_GISB_ARB, instead, just let it be default ARCH_BRCMSTB which is
a better way to deal with this. While at it, also make it default
BMIPS_GENERIC so the legacy MIPS-based STB platforms can benefit from
the same thing.
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>

arch/arm/mach-bcm/Kconfig

@@ -173,7 +173,6 @@ config ARCH_BRCMSTB
 	select ARM_GIC
 	select ARM_ERRATA_798181 if SMP
 	select HAVE_ARM_ARCH_TIMER
-	select BRCMSTB_GISB_ARB
 	select BRCMSTB_L2_IRQ
 	select BCM7120_L2_IRQ
 	select ARCH_DMA_ADDR_T_64BIT if ARM_LPAE

drivers/bus/Kconfig

@@ -58,6 +58,7 @@ config ARM_CCN
 config BRCMSTB_GISB_ARB
 	bool "Broadcom STB GISB bus arbiter"
 	depends on ARM || MIPS
+	default ARCH_BRCMSTB || BMIPS_GENERIC
 	help
 	  Driver for the Broadcom Set Top Box System-on-a-chip internal bus
 	  arbiter. This driver provides timeout and target abort error handling