[RFCv3 2/4] xhci: Add a global command queue

Create a list to store command structures, add a structure to it every time a command is submitted, and remove it from the list once we get a command completion event matching the command. Callers that wait for completion will free their command structures themselves. The other command structures

[RFCv3 2/4] xhci: Add a global command queue

Create a list to store command structures, add a structure to it every time a command is submitted, and remove it from the list once we get a command completion event matching the command. Callers that wait for completion will free their command structures themselves. The other command structures