memory_bus: Split register mapping into own function

Now that we have a hook for the memory mapping, we don't need
FEATURE_REGISTERMAP anymore and can clean up around it.

Change-Id: If11ece9ce81ddf214b75764007a1006d271dc8af
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.sourcearcade.org/c/flashprog/+/72523
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
4 files changed