MIPS: boston: Migrate to OF_UPSTREAM

We can now boot with upstream devicetree.

Reviewed-by: Sumit Garg <sumit.garg@linaro.org>
Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Reviewed-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index 748b517..733a8de 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -146,6 +146,7 @@
 	select SUPPORTS_CPU_MIPS64_R2
 	select SUPPORTS_CPU_MIPS64_R6
 	select SUPPORTS_LITTLE_ENDIAN
+	imply OF_UPSTREAM
 	imply BOOTSTD_FULL
 	imply CLK
 	imply CLK_BOSTON