[misc] Fix building on OpenBSD

OpenBSD throws compiler warnings that we can't reproduce on Linux, for
some reason.

Original patch from Dewey Hylton <dewey@hyltown.com>.

src/image/embedded.c

  * data structure.
  */
 
-#include <stdio.h>
 #include <gpxe/image.h>
 #include <gpxe/malloc.h>
 #include <gpxe/uaccess.h>
 	if ( reclaimed )
 		return NULL;	/* Already reclaimed */
 
-	printf("Embedded image: %d bytes at %p\n",
-	       eisize, _embedded_image_start);
+	DBG ( "Embedded image: %zd bytes at %p\n",
+	      eisize, _embedded_image_start );
 
 	image = alloc_image();
 	if (!image)

src/interface/pxe/pxe_tftp.c

 	if ( blksize < TFTP_DEFAULT_BLKSIZE )
 		blksize = TFTP_DEFAULT_BLKSIZE;
 	snprintf ( uri_string, sizeof ( uri_string ),
-		   "tftp://%s:%d%s%s?blksize=%d",
+		   "tftp://%s:%d%s%s?blksize=%zd",
 		   inet_ntoa ( address ), ntohs ( port ),
 		   ( ( filename[0] == '/' ) ? "" : "/" ), filename, blksize );
 	DBG ( " %s", uri_string );