squash! WIP: add rnndb for MDP40.. some tweaks
squash! WIP: add rnndb for MDP40

Remove variants for now.. possibly we want variants for revisions of
mdp4, but different db files for mdp3, mdss, etc.  Not sure how similar
the different display controller blocks are, but I think it makes more
sense to try and deal with variants once the differences are better
understood.

And rename mdp->mdp4
rnn: add support for symbolic array indices

This probably isn't quite right for nested arrays.. not quite sure the
best way to handle that.
headergen2: add support for symbolic array indices
rnn: add support for irregular arrays

Add support for "arrays" with non-regular base addresses.  Sometimes hw
designers put identical blocks of registers in goofy places.  But for
writing a driver or looking at decoded traces, it is easier to think of
it as conceptually an array.

(TODO: headergen is not updated for this yet, since I don't use it..)
headergen2: add support for irregular arrays
squash! WIP: add rnndb for MDP40