[linux-kernel] Separate xxhash into its own module

contrib/linux-kernel/lib/zstd/Makefile

@@ -3,7 +3,7 @@ obj-$(CONFIG_ZSTD_DECOMPRESS) += zstd_decompress.o
 
 ccflags-y += -O3
 
-zstd_compress-y := entropy_common.o fse_decompress.o xxhash.o zstd_common.o \
+zstd_compress-y := entropy_common.o fse_decompress.o zstd_common.o \
 				fse_compress.o huf_compress.o compress.o
-zstd_decompress-y := entropy_common.o fse_decompress.o xxhash.o zstd_common.o \
+zstd_decompress-y := entropy_common.o fse_decompress.o zstd_common.o \
 				huf_decompress.o decompress.o