Library is not re-entrant

[xross]

Cannot easily use the library with a device with 2 x USB phys - XU232 for example.

[ed-xmos]

We have experimental solutions for this now - https://xmosjira.atlassian.net/wiki/spaces/UAAI/pages/3926720542/Feasibility+for+multi-XUD+and+XUA+projects