[ast] split ast os to power domains

[meisnere]

This PR should be used as a reference when building the new top level structure.
Eventually, ast_aon should be under <name>_pd_aon, and ast_main should be under <name>_pd_main while ast hierarchy itself would be deprecated.

The PR can be merged as is until top level restructuring is completed.

This PR was tested by the following tests and yielded the same results as before:

100% pass rate:
  chip_sw_ast_clk_outputs
  chip_sw_clkmgr_reset_frequency 
  chip_sw_clkmgr_sleep_frequency 
  chip_sw_pwrmgr_sleep_sensor_ctrl_alert_wakeup
 
depends on seed:
  chip_sw_sensor_ctrl_alert
 
fails:
  chip_sw_ast_clk_rst_inputs

make -C hw top
make -C hw top_earlgrey_gen

[elliotb-lowrisc]

It seems some old typos have been reintroduced, possibly due to some of the typos not being fixed in the source of auto-generated (by a closed-source generator) code.

I have not reviewed the main content of this PR as I do not think I am knowledgeable enough on the AST at this time.

[meisnere]

It seems some old typos have been reintroduced, possibly due to some of the typos not being fixed in the source of auto-generated (by a closed-source generator) code.

I have not reviewed the main content of this PR as I do not think I am knowledgeable enough on the AST at this time.

@elliotb-lowrisc Good catch! Just pushed a fix to the AST source :)

[elliotb-lowrisc]

I've looked a bit more and found some other things I'm not sure about. Still more to look through, which might be easier if this rather large commit was broken up into smaller ones.

You'll also need to add a sign-off line to the commit/commits as per the contributor guidelines here: https://github.com/lowRISC/opentitan/blob/master/CONTRIBUTING.md

[vogelpi]

I've just this PR with @meisnere. The intention is not to merge this right now but to give people an idea of how the split AST will look like. Having this allows us to do, e.g., the tooling work required for pulling ast into the top(s) (right now the ast is outside of the top, but it will be moved into top_aon and top_main in the future, see RFC: Aon Power Domain Reorganization).

Also, we should not merge this PR right now, as it may complicate DV work happening in the closed source right now.

For these reasons, I have now converted the PR to draft.