boot: Support compressed booti images in bootm

A compressed booti image relies on the compression-format's header at
the start to indicate which compression algorithm is used.

We don't support this elsewhere in U-Boot, so assume that a compressed
file is always a booti file. Once it is compressed, a check is made to
make sure that it actually is.

Simplify the implementation by adding a new function which returns the
booti image-type if compression is detected.

Signed-off-by: Simon Glass <sjg@chromium.org>

include/image.h

@@ -648,6 +648,17 @@ ulong genimg_get_kernel_addr(char * const img_addr);
  */
 enum image_fmt_t genimg_get_format(const void *img_addr);
 
+/**
+ * genimg_get_format_comp() - Like genimg_get_format() but adds compressed booti
+ *
+ * If a compressed file is detected (with image_decomp_type()) and
+ * CONFIG_CMD_BOOTI is enabled, then this returns IMAGE_FORMAT_BOOTI
+ *
+ * @img_addr: image start address
+ * Return: image format type or IMAGE_FORMAT_INVALID if no image is present
+ */
+enum image_fmt_t genimg_get_format_comp(const void *img_addr);
+
 int genimg_has_config(struct bootm_headers *images);
 
 /**