top/polysyn/tusb322i: enable VBUS when enumerating as Accessory/DebugDfp

[vk2seb]

Fix for #170 - some USB C devices enumerate as DebugDfp and weren't supplied with VBUS.

From the code --

It seems some USB-C adapters will enumerate as a DebugDfp accessory. Enabling VBUS
is still safe in this situation, as we can only land in DebugDfp if the CC
controller is sure we are a DFP. It's not sufficient to just check
Attached.ACCESSORY as we could also enumerate as an UFP accessory against a host!

As for WHY some devices are enumerating as a DebugDfp, it would be good to have an answer. I need to break out the CY4500 at some point and trace one these 'bad' devices. It may be something to do with how we are driving VBUS, as we have our own state machine outside the tusb322i

UPDATE: results of the CY4500 investigation here: apfaudio/tiliqua-hardware#1

[vk2seb]

closes #170