MIPS: bcm47xx: enable ZBOOT support

Enable ZBOOT support. The WRT54GL router's bootloader limits kernel
size to 3 MB with the normal load address, which is a bit challenging
vmlinux size with modern Linux. A compressed kernel allows booting
much bigger kernels.
Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Hauke Mehrtens <hauke@hauke-m.de>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/18492/Signed-off-by: James Hogan <jhogan@kernel.org>

arch/mips/Kconfig

@@ -253,6 +253,7 @@ config BCM47XX
 	select SYS_SUPPORTS_32BIT_KERNEL
 	select SYS_SUPPORTS_LITTLE_ENDIAN
 	select SYS_SUPPORTS_MIPS16
+	select SYS_SUPPORTS_ZBOOT
 	select SYS_HAS_EARLY_PRINTK
 	select USE_GENERIC_EARLY_PRINTK_8250
 	select GPIOLIB

arch/mips/bcm47xx/Platform

@@ -5,3 +5,4 @@ platform-$(CONFIG_BCM47XX)	+= bcm47xx/
 cflags-$(CONFIG_BCM47XX)	+=					\
 		-I$(srctree)/arch/mips/include/asm/mach-bcm47xx
 load-$(CONFIG_BCM47XX)		:= 0xffffffff80001000
+zload-$(CONFIG_BCM47XX)		+= 0xffffffff80400000