[image] Add the concept of a static image

Not all images are allocated via alloc_image().  For example: embedded
images, the static images created to hold a runtime command line, and
the images used by unit tests are all static structures.

Using image_set_cmdline() (via e.g. the "imgargs" command) to set the
command-line arguments of a static image will succeed but will leak
memory, since nothing will ever free the allocated command line.
There are no code paths that can lead to calling image_set_len() on a
static image, but there is no safety check against future code paths
attempting this.

Define a flag IMAGE_STATIC to mark an image as statically allocated,
generalise free_image() to also handle freeing dynamically allocated
portions of static images (such as the command line), and expose
free_image() for use by static images.

Define a related flag IMAGE_STATIC_NAME to mark the name as statically
allocated.  Allow a statically allocated name to be replaced with a
dynamically allocated name since this is a potentially valid use case
(e.g. if "imgdecrypt --name <name>" is used on an embedded image).

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/tests/pixbuf_test.h

@@ -41,6 +41,7 @@ struct pixel_buffer_test {
 	static struct image _name ## __image = {			\
 		.refcnt = REF_INIT ( ref_no_free ),			\
 		.name = #_name,						\
+		.flags = ( IMAGE_STATIC | IMAGE_STATIC_NAME ),		\
 		.data = ( userptr_t ) ( _name ## __file ),		\
 		.len = sizeof ( _name ## __file ),			\
 	};								\