pxe: Move pxe_utils files

Move the header file into the main include/ directory so we can use it
from the bootmethod code. Move the C file into boot/ since it relates to
booting.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Artem Lapkin <email2tema@gmail.com>
Tested-by: Artem Lapkin <email2tema@gmail.com>
Reviewed-by: Ramon Fried <rfried.dev@gmail.com>

cmd/sysboot.c

@@ -4,7 +4,7 @@
 #include <command.h>
 #include <env.h>
 #include <fs.h>
-#include "pxe_utils.h"
+#include <pxe_utils.h>
 
 static char *fs_argv[5];