Overhaul bootmagic logic to have single entrypoint (#8532)

* Relocate bootmagic logic to have single entrypoint

* Align init of layer state

quantum/bootmagic/bootmagic.h

@@ -0,0 +1,24 @@
+/* Copyright 2021 QMK
+ *
+ * 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 3 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
+
+#if defined(BOOTMAGIC_ENABLE)
+#    include "bootmagic_full.h"
+#elif defined(BOOTMAGIC_LITE)
+#    include "bootmagic_lite.h"
+#endif
+
+void bootmagic(void);