[efi] Add "reboot" command for EFI

Abstract out the ability to reboot the system to a separate reboot()
function (with platform-specific implementations), add an EFI
implementation, and make the existing "reboot" command available under
EFI.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/config/reboot.h

@@ -0,0 +1,16 @@
+#ifndef CONFIG_REBOOT_H
+#define CONFIG_REBOOT_H
+
+/** @file
+ *
+ * Reboot API configuration
+ *
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER );
+
+#include <config/defaults.h>
+
+#include <config/local/reboot.h>
+
+#endif /* CONFIG_REBOOT_H */