mips: ralink: enable zboot support

Some of these ralink devices come with an ancient u-boot which can't
extract LZMA properly when image gets too big.
Enable zboot support to get a self-extracting kernel instead of relying
on broken u-boot support.

Signed-off-by: Chuanhong Guo <gch981213@gmail.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

arch/mips/Kconfig

@@ -616,6 +616,7 @@ config RALINK
 	select SYS_SUPPORTS_32BIT_KERNEL
 	select SYS_SUPPORTS_LITTLE_ENDIAN
 	select SYS_SUPPORTS_MIPS16
+	select SYS_SUPPORTS_ZBOOT
 	select SYS_HAS_EARLY_PRINTK
 	select CLKDEV_LOOKUP
 	select ARCH_HAS_RESET_CONTROLLER