loader: fdt: Add fdt_is_setup function

When efi_autoload is called it will call fdt_setup_fdtp which setup the
dtb and overlays. If a user already loaded at dtb or overlays or just
printed the efi provided dtb, this will re-setup everything and also
re-applying the overlays.
Test that everything is setup before doing it again.

Reviewed by:	kevans
Differential Revision:	https://reviews.freebsd.org/D20059

stand/efi/loader/autoload.c

@@ -50,7 +50,8 @@ efi_autoload(void)
 	 * imply that we're on a platform where FDT is a requirement.  If we
 	 * fix this, then the error handling here should be fixed accordingly.
 	 */
-	fdt_setup_fdtp();
+	if (fdt_is_setup() == 0)
+		fdt_setup_fdtp();
 #endif
 	return (0);
 }

stand/fdt/fdt_loader_cmd.c

@@ -509,6 +509,16 @@ fdt_apply_overlays()
 	free(overlay);
 }
 
+int
+fdt_is_setup(void)
+{
+
+	if (fdtp != NULL)
+		return (1);
+
+	return (0);
+}
+
 int
 fdt_setup_fdtp()
 {

stand/fdt/fdt_platform.h

@@ -48,6 +48,7 @@ int fdt_load_dtb_addr(struct fdt_header *);
 int fdt_load_dtb_file(const char *);
 void fdt_load_dtb_overlays(const char *);
 int fdt_setup_fdtp(void);
+int fdt_is_setup(void);
 
 /* The platform library needs to implement these functions */
 int fdt_platform_load_dtb(void);