common: Add a new lz4.h header file

Add a header file to house the lz4 compression function. Add a comment
while we are here, since it not even clear from the name what the function
actuall does.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>

common/image.c

@@ -20,6 +20,7 @@
 
 #include <gzip.h>
 #include <image.h>
+#include <lz4.h>
 #include <mapmem.h>
 
 #if IMAGE_ENABLE_FIT || IMAGE_ENABLE_OF_LIBFDT