mkimage: Make genimg_print_size() global

Currently it is used by image.c only, but the the function can be
used to support additional mkimage types like for example kwbimage,
so make this function globally visible.

Signed-off-by: Prafulla Wadaskar <prafulla@marvell.com>

Edited commit message.

Signed-off-by: Wolfgang Denk <wd@denx.de>
diff --git a/include/image.h b/include/image.h
index a62669f..4a7bf78 100644
--- a/include/image.h
+++ b/include/image.h
@@ -292,6 +292,7 @@
 int genimg_get_arch_id (const char *name);
 int genimg_get_type_id (const char *name);
 int genimg_get_comp_id (const char *name);
+void genimg_print_size (uint32_t size);
 
 #ifndef USE_HOSTCC
 /* Image format types, returned by _get_format() routine */