ADIv5: doxygen
Provide doxygen for many of the public ADIv5 interfaces (i.e. the ones
called from Cortex core support code).
Add FIXMEs (and a TODO) to help resolve implementation issues which
became more apparent when trying to document this code:
- Error-prone context-sensitivity (queued/nonqueued) in many procedures.
- Procedures that lie by ignoring errors and wrongly claiming success.
Also, there was no point in a return from dap_ap_select(); it can't fail,
and no caller checks its return status. Clean that up, make it void.
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>