dipswitch.c: Rename src and header file

- (non function-changing update) just for consistency, append "libretro_" to source file to be consistent with new core option file

src/drivers/libretro/libretro_dipswitch.h

@@ -0,0 +1,12 @@
+#ifndef __VSUNI_DIPSWITCH__
+#define __VSUNI_DIPSWITCH__
+
+#include <libretro.h>
+
+size_t set_dipswitch_variables(unsigned current_index, struct retro_core_option_definition *vars);
+void update_dipswitch(void);
+void DPSW_Cleanup(void);
+
+extern retro_environment_t environ_cb;
+
+#endif /* __VSUNI_DIPSWITCH__ */