A few more items for the glossary, and understanding GPU switching

[Yann Dirson]

Adding to the list:

* ACA, mentionned in debug_mask flags - digging the source shows it seems to be
  "Accelerator Check Architecture", but maybe some additional details could be
  added?
* DPIA (likely for dc-glossary): listed in DC_DEBUG_MASK values, source code
  in several places shows "DisplayPort Input Adapter", but maybe more details would
  be useful here too?  Often associated with DP USB4 tunneling in source code.

Best regards,
-- 
Yann