Re-structure splinky support to handle versioning in the same fashion as for the teensy (#19123)

keyboards/bastardkb/charybdis/4x6/v2/splinky_2/mcuconf.h

@@ -0,0 +1,23 @@
+/*
+ * Copyright 2022 Charly Delay <charly@codesink.dev> (@0xcharly)
+ *
+ * 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_next "mcuconf.h"
+
+#undef RP_SPI_USE_SPI0
+#define RP_SPI_USE_SPI0 TRUE