memory_bus: Move related declarations into new `chipdrivers/memory_bus.h`

Change-Id: I2bef65de77860d049ec3d9938ae777c5f929c258
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.sourcearcade.org/c/flashprog/+/438
diff --git a/w39.c b/w39.c
index f58c495..234bcd8 100644
--- a/w39.c
+++ b/w39.c
@@ -16,7 +16,7 @@
  */
 
 #include "flash.h"
-#include "chipdrivers.h"
+#include "chipdrivers/memory_bus.h"
 
 static uint8_t w39_idmode_readb(struct flashctx *flash, unsigned int offset)
 {