gzip: add a function to parse the header

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

include/common.h

@@ -609,6 +609,7 @@ ulong	usec2ticks    (unsigned long usec);
 ulong	ticks2usec    (unsigned long ticks);
 
 /* lib/gunzip.c */
+int gzip_parse_header(const unsigned char *src, unsigned long len);
 int gunzip(void *, int, unsigned char *, unsigned long *);
 int zunzip(void *dst, int dstlen, unsigned char *src, unsigned long *lenp,
 						int stoponerr, int offset);