lz4: Use a private header for U-Boot

At present U-Boot has a header file called lz4.h for its own use. If the
host has its own lz4 header file installed (e.g. from the 'liblz4-dev'
package) then host builds will use that instead.

Move the U-Boot file into its own directory, as is done with various
other headers with the same problem.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/cmd/unlz4.c b/cmd/unlz4.c
index 323ab46..5f20838 100644
--- a/cmd/unlz4.c
+++ b/cmd/unlz4.c
@@ -7,7 +7,7 @@
 #include <common.h>
 #include <command.h>
 #include <env.h>
-#include <lz4.h>
+#include <u-boot/lz4.h>
 
 static int do_unlz4(struct cmd_tbl *cmdtp, int flag, int argc,
 		    char *const argv[])