linux: enable uBoot image type for xtensa kernel

Starting with the release 2016.09 xtensa architecture is supported by
the U-Boot. Enable uimage target in xtensa linux kernel.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

linux/Config.in

@@ -179,7 +179,7 @@ config BR2_LINUX_KERNEL_UIMAGE
 	depends on BR2_arc || BR2_arm || BR2_armeb || BR2_bfin || \
 		   BR2_powerpc || BR2_powerpc64 || BR2_powerpc64le || \
 		   BR2_sh || BR2_mips || BR2_mipsel || \
-		   BR2_mips64 || BR2_mips64el
+		   BR2_mips64 || BR2_mips64el || BR2_xtensa
 	select BR2_LINUX_KERNEL_UBOOT_IMAGE
 
 config BR2_LINUX_KERNEL_APPENDED_UIMAGE