[util/topgen] Top module generator

[eunchan]

The goals of the task are:

1. To define top configuration hjson format.
2. To generate top-level connection RTL, which has following modules, crossbars, peripherals, processor block, alert handler, pinmux, and padring (having multiple PAD instances).
3. To give editable template of the top module. Most of the top module is generated by the tool but it gives flexibility to include sub template files at the couple of the point. For instance, uart.header.svh file may be included in front of uart instantiation.

Document: https://docs.google.com/document/d/1LKzddc7UlF_avTnY1MZ0PFcrhzKkfvW1coZrREht72s/edit?usp=sharing

[sjgitty]

Still pending: alert handler, pinmux, and pad control

[aytong]

@eunchan , once #477 goes in, can this then be marked as closed?

[eunchan]

Nope not yet. Still alert_handler and padctrl are pending.

[msfschaffner]

@eunchan I believe this one can be closed, right?