ARC: build: add uImage.lzma to the top-level target

[ Upstream commit f2712ec76a5433e5ec9def2bd52a95df1f96d050 ]

arch/arc/boot/Makefile supports uImage.lzma, but you cannot do
'make uImage.lzma' because the corresponding target is missing
in arch/arc/Makefile. Add it.

I also changed the assignment operator '+=' to ':=' since this is the
only place where we expect this variable to be set.

Signed-off-by: Masahiro Yamada <[email protected]>
Signed-off-by: Vineet Gupta <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>
diff --git a/arch/arc/Makefile b/arch/arc/Makefile
index acf9942..61a4112 100644
--- a/arch/arc/Makefile
+++ b/arch/arc/Makefile
@@ -102,7 +102,7 @@
 
 boot		:= arch/arc/boot
 
-boot_targets += uImage uImage.bin uImage.gz
+boot_targets := uImage uImage.bin uImage.gz uImage.lzma
 
 $(boot_targets): vmlinux
 	$(Q)$(MAKE) $(build)=$(boot) $(boot)/$@