[bzimage] Kill off the initrd image type

We can just treat all non-kernel images as initrds, which matches our
behaviour for multiboot kernels.  This allows us to eliminate initrd as
an image type, and treat the "initrd" command as just another synonym for
"imgfetch".

src/arch/i386/image/bzimage.c

@@ -34,7 +34,6 @@
 #include <gpxe/image.h>
 #include <gpxe/segment.h>
 #include <gpxe/init.h>
-#include <gpxe/initrd.h>
 #include <gpxe/cpio.h>
 #include <gpxe/features.h>
 
@@ -188,8 +187,8 @@ static size_t bzimage_load_initrd ( struct image *image,
 	struct cpio_header cpio;
         size_t offset = 0;
 
-	/* Ignore images which aren't initrds */
-	if ( initrd->type != &initrd_image_type )
+	/* Do not include kernel image itself as an initrd */
+	if ( initrd == image )
 		return 0;
 
 	/* Create cpio header before non-prebuilt images */

src/hci/commands/image_cmd.c

@@ -24,7 +24,6 @@
 #include <getopt.h>
 #include <gpxe/image.h>
 #include <gpxe/command.h>
-#include <gpxe/initrd.h>
 #include <usr/imgmgmt.h>
 
 /** @file
@@ -222,23 +221,6 @@ static int kernel_exec ( int argc, char **argv ) {
 	return 0;
 }
 
-/**
- * The "initrd" command
- *
- * @v argc		Argument count
- * @v argv		Argument list
- * @ret rc		Exit code
- */
-static int initrd_exec ( int argc, char **argv ) {
-	int rc;
-
-	if ( ( rc = imgfetch_core_exec ( &initrd_image_type, IMG_FETCH,
-					 argc, argv ) ) != 0 )
-		return rc;
-
-	return 0;
-}
-
 /**
  * "imgload" command syntax message
  *
@@ -557,12 +539,12 @@ struct command image_commands[] __command = {
 		.exec = imgfetch_exec, /* synonym for "imgfetch" */
 	},
 	{
-		.name = "kernel",
-		.exec = kernel_exec,
+		.name = "initrd",
+		.exec = imgfetch_exec, /* synonym for "imgfetch" */
 	},
 	{
-		.name = "initrd",
-		.exec = initrd_exec,
+		.name = "kernel",
+		.exec = kernel_exec,
 	},
 	{
 		.name = "imgload",