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/arch/mips/mach-mtmips/mt7621/spl/spl.c b/arch/mips/mach-mtmips/mt7621/spl/spl.c
index 91eebc6..aa5b267 100644
--- a/arch/mips/mach-mtmips/mt7621/spl/spl.c
+++ b/arch/mips/mach-mtmips/mt7621/spl/spl.c
@@ -64,7 +64,7 @@
 unsigned long spl_nor_get_uboot_base(void)
 {
 	const struct tpl_info *tpli;
-	const image_header_t *hdr;
+	const struct legacy_img_hdr *hdr;
 	u32 addr;
 
 	addr = FLASH_MMAP_BASE + TPL_INFO_OFFSET;
@@ -72,7 +72,7 @@
 
 	if (tpli->magic == TPL_INFO_MAGIC) {
 		addr = FLASH_MMAP_BASE + tpli->size;
-		hdr = (const image_header_t *)KSEG1ADDR(addr);
+		hdr = (const struct legacy_img_hdr *)KSEG1ADDR(addr);
 
 		if (image_get_magic(hdr) == IH_MAGIC) {
 			addr += sizeof(*hdr) + image_get_size(hdr);