Soc peripherals improvements

[meggiman]

This PR contains a collection of improvements to the soc peripheral infrastructure and the SoC in general assembled from the last couple of tapeouts. Here is a list of changes:

• The udma subsystem has been wrapped in a different repo and now only exposes struct based IO signals for simpler through-hierarchy routing
• The old apb_gpio peripheral has been replaced with the more modern and feature enhanced version from pulp-platfrom/gpio
• Externalization of the clock generation logic
• Removal of unused signals and fixing of various linter warnings
• Externalization of reset synchronization

This PR introduces breaking changes to the top-level interface of pulp-soc.

[meggiman]

This PR depends on outstanding PR https://github.com/pulp-platform/pulp-io/pull/1