[Keyboard] Atreus: add STM32F103C8T6 based variant (#16846)

Co-authored-by: Ryan <fauxpark@gmail.com>

keyboards/atreus/f103/config.h

@@ -0,0 +1,38 @@
+/* Copyright 2022 DmNosachev
+ *
+ * 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 "config_common.h"
+
+/*
+ * Keyboard Matrix Assignments
+ *
+ * Change this to how you wired your keyboard
+ * COLS: AVR pins used for columns, left to right
+ * ROWS: AVR pins used for rows, top to bottom
+ * DIODE_DIRECTION: COL2ROW = COL = Anode (+), ROW = Cathode (-, marked on diode)
+ *                  ROW2COL = ROW = Anode (+), COL = Cathode (-, marked on diode)
+ *
+*/
+
+/* key matrix pins */
+#define MATRIX_COL_PINS { B10, B1, B0, A7, A6, B5, B4, B3, A15, A10, A9 }
+#define MATRIX_ROW_PINS { A5, A4, A3, A2 }
+#define UNUSED_PINS {B12, B13, B14, B15, A8, B6, B7, B8, B9, A1, A0, C15, C14, C13}
+
+/* COL2ROW, ROW2COL*/
+#define DIODE_DIRECTION COL2ROW