lib: zstd: clean up Makefile for simpler composite object handling

Now, Kbuild nicely handles composite objects to avoid multiple
definition.

Makefiles can simply add the same objects multiple times across
composite objects.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

lib/zstd/Makefile

@@ -3,16 +3,7 @@ obj-$(CONFIG_ZSTD_DECOMPRESS) += zstd_decompress.o
 
 ccflags-y += -O3
 
-# Object files unique to zstd_compress and zstd_decompress
-zstd_compress-y := fse_compress.o huf_compress.o compress.o
-zstd_decompress-y := huf_decompress.o decompress.o
-
-# These object files are shared between the modules.
-# Always add them to zstd_compress.
-# Unless both zstd_compress and zstd_decompress are built in
-# then also add them to zstd_decompress.
-zstd_compress-y += entropy_common.o fse_decompress.o zstd_common.o
-
-ifneq ($(CONFIG_ZSTD_COMPRESS)$(CONFIG_ZSTD_DECOMPRESS),yy)
-	zstd_decompress-y += entropy_common.o fse_decompress.o zstd_common.o
-endif
+zstd_compress-y := fse_compress.o huf_compress.o compress.o \
+		   entropy_common.o fse_decompress.o zstd_common.o
+zstd_decompress-y := huf_decompress.o decompress.o \
+		     entropy_common.o fse_decompress.o zstd_common.o