efi_loader: ResetSystem() should not hang

If ResetSystem() is not implemented at runtime, it should return instead
of hanging in an endless loop. This allows the operating system to reset
the system by other means as Linux does. It also matches what EDK II
suggests in comments for functions ResetShutdown() and ResetWarm() in
OvmfPkg/Library/ResetSystemLib/ResetSystemLib.c.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>

lib/efi_loader/efi_runtime.c

@@ -365,7 +365,9 @@ out:
  * efi_reset_system() - reset system
  *
  * This function implements the ResetSystem() runtime service after
- * SetVirtualAddressMap() is called. It only executes an endless loop.
+ * SetVirtualAddressMap() is called. As this placeholder cannot reset the
+ * system it simply return to the caller.
+ *
  * Boards may override the helpers below to implement reset functionality.
  *
  * See the Unified Extensible Firmware Interface (UEFI) specification for
@@ -381,8 +383,7 @@ void __weak __efi_runtime EFIAPI efi_reset_system(
 			efi_status_t reset_status,
 			unsigned long data_size, void *reset_data)
 {
-	/* Nothing we can do */
-	while (1) { }
+	return;
 }
 
 /**