[Keyboard] Add Split65 to keyboards/handwired (#13264)

Co-authored-by: Drashna Jaelre <drashna@live.com>
Co-authored-by: Ryan <fauxpark@gmail.com>
Co-authored-by: Joris Wachsmuth <jwachsmuth@techfak.uni-bielefeld.de>

keyboards/handwired/split65/split65.h

@@ -0,0 +1,24 @@
+/* Copyright 2020-2021 PercyJW-2 <joris.wachsmuth@gmail.com>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#pragma once
+
+#include "quantum.h"
+
+#if defined(KEYBOARD_handwired_split65_stm32)
+    #include "stm32.h"
+#elif defined(KEYBOARD_handwired_split65_promicro)
+    #include "promicro.h"
+#endif