memory_bus: Move (un)map_flash_region into par master

Now that the map/unmap_flash functions are only called from memory-
mapped chip drivers, we can safely move the hooks into the parallel
masters.

This also allows us to move the code away from the globals in
`flashprog.c` into a new `memory_bus.c`.

Change-Id: Ic476cf4d96200232900537b997e1d07bb4e8b809
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.sourcearcade.org/c/flashprog/+/72522
Reviewed-by: Riku Viitanen <riku.viitanen@protonmail.com>
diff --git a/internal.c b/internal.c
index f8de4a7..5d85758 100644
--- a/internal.c
+++ b/internal.c
@@ -84,6 +84,8 @@
 	.chip_writew	= internal_chip_writew,
 	.chip_writel	= internal_chip_writel,
 	.chip_writen	= fallback_chip_writen,
+	.map_flash	= physmap,
+	.unmap_flash	= physunmap,
 };
 
 enum chipbustype internal_buses_supported = BUS_NONE;
@@ -362,6 +364,4 @@
 	.type			= OTHER,
 	.devs.note		= NULL,
 	.init			= internal_init,
-	.map_flash_region	= physmap,
-	.unmap_flash_region	= physunmap,
 };