treewide: Drop image_header_t typedef

This is not needed and we should avoid typedefs. Use the struct instead
and rename it to indicate that it really is a legacy struct.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/common/spl/spl_mmc.c b/common/spl/spl_mmc.c
index 23a395e..e4135b2 100644
--- a/common/spl/spl_mmc.c
+++ b/common/spl/spl_mmc.c
@@ -20,7 +20,7 @@
 static int mmc_load_legacy(struct spl_image_info *spl_image,
 			   struct spl_boot_device *bootdev,
 			   struct mmc *mmc,
-			   ulong sector, struct image_header *header)
+			   ulong sector, struct legacy_img_hdr *header)
 {
 	u32 image_offset_sectors;
 	u32 image_size_sectors;
@@ -83,7 +83,7 @@
 			      struct mmc *mmc, unsigned long sector)
 {
 	unsigned long count;
-	struct image_header *header;
+	struct legacy_img_hdr *header;
 	struct blk_desc *bd = mmc_get_blk_desc(mmc);
 	int ret = 0;