[source] u-boot.mk: add support for overriding DEFAULT

[LEDE Commits]

nbd pushed a commit to source.git, branch master:
https://git.lede-project.org/1c0addb15608b7a0d73fd056524f505df02eb5e3

commit 1c0addb15608b7a0d73fd056524f505df02eb5e3
Author: Felix Fietkau <nbd at nbd.name>
AuthorDate: Wed Jan 25 07:33:41 2017 +0100

    u-boot.mk: add support for overriding DEFAULT
    
    Signed-off-by: Felix Fietkau <nbd at nbd.name>
---
 include/u-boot.mk | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/include/u-boot.mk b/include/u-boot.mk
index de62923..0c28653 100644
--- a/include/u-boot.mk
+++ b/include/u-boot.mk
@@ -32,6 +32,7 @@ define U-Boot/Init
   NAME:=
   DEPENDS:=
   HIDDEN:=
+  DEFAULT:=
   VARIANT:=$(1)
   UBOOT_CONFIG:=$(1)
   UBOOT_IMAGE:=u-boot.bin
@@ -59,6 +60,7 @@ define Build/U-Boot/Target
 		$(patsubst %,|| $(patsubst TARGET_%,TARGET_DEVICE_%,$(TARGET_DEP))_DEVICE_%,$(BUILD_DEVICES)))
       endif
     endif
+    $(if $(DEFAULT),DEFAULT:=$(DEFAULT))
     URL:=http://www.denx.de/wiki/U-Boot
   endef