memory_bus: Turn flashbase into a par_master member `rom_base`

Get rid of the global `flashbase`. Treat overrides for the `rom_base`
similar to `max_rom_decode`: Gather the information in `internal_data`
and then pass it to register_par_master().

Change-Id: Ib9ed7234a849fe3550200fd602226d0036da15f0
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.sourcearcade.org/c/flashprog/+/436
diff --git a/drkaiser.c b/drkaiser.c
index 6fcb5d2..5634b3a 100644
--- a/drkaiser.c
+++ b/drkaiser.c
@@ -74,7 +74,7 @@
 	if (drkaiser_bar == ERROR_PTR)
 		return 1;
 
-	return register_par_master(&par_master_drkaiser, BUS_PARALLEL, 128*KiB, NULL);
+	return register_par_master(&par_master_drkaiser, BUS_PARALLEL, 0, 128*KiB, NULL);
 }
 
 static void drkaiser_chip_writeb(const struct flashctx *flash, uint8_t val,