[source] u-boot.mk: add UBOOT_MAKE_FLAGS variable similar to MAKE_FLAGS

[LEDE Commits]

nbd pushed a commit to source.git, branch master:
https://git.lede-project.org/1e14f01ed6d0cfff962c633bf130e96964c13e43

commit 1e14f01ed6d0cfff962c633bf130e96964c13e43
Author: Felix Fietkau <nbd at nbd.name>
AuthorDate: Wed Jan 25 07:28:57 2017 +0100

    u-boot.mk: add UBOOT_MAKE_FLAGS variable similar to MAKE_FLAGS
    
    Signed-off-by: Felix Fietkau <nbd at nbd.name>
---
 include/u-boot.mk | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/u-boot.mk b/include/u-boot.mk
index 4993eb6..de62923 100644
--- a/include/u-boot.mk
+++ b/include/u-boot.mk
@@ -76,7 +76,8 @@ DTC=$(wildcard $(LINUX_DIR)/scripts/dtc/dtc)
 define Build/Compile/U-Boot
 	+$(MAKE) $(PKG_JOBS) -C $(PKG_BUILD_DIR) \
 		CROSS_COMPILE=$(TARGET_CROSS) \
-		$(if $(DTC),DTC="$(DTC)")
+		$(if $(DTC),DTC="$(DTC)") \
+		$(UBOOT_MAKE_FLAGS)
 endef
 
 define BuildPackage/U-Boot/Defaults