Print addresses for submaps in struct constant files

[lorenzschmid]

Currently, there are two types of constant files that can be generated in proto/cheby/print_consts.py:

• ConstsVisitor
• StructVisitor

For the later, each bit field is generated as a structure linked to its parent elements, e.g. in Matlab we get for a single field:

REG_TOP.status.idle.WIDTH = 1;
REG_TOP.status.idle.OFFSET = 0;
REG_TOP.status.idle.WIDTH = 1;

For any entry that is not a bit field such as submaps, no structure or constant is generated. This is particularly a problem when using nested register maps. This PR proposes now to include as the very least the address for submaps, e.g.

REG_TOP.submap.ADDR = 256;