forget to add test file for ehci isr
add hard fault handler to bsp.c
rename class_install_subtask to class_open_subtask
add class_close for unmount
adding code for usbh_device_unplugged_isr & invoke it in hcd_isr
add usbh_pipe_control_close (in conjunction with usbh pipe control open)
close control pipe when unplugged
refractor ehci test files
adding some code for async_advance_isr
add test for async_advance_isr
refractor rename field inactive_next_xact of ehci_qhd_t
add some test for usbh_hcd integration
- add tests for pipe_close  (while TDs are active)
- add tests for device unplugged
add tesst & implement the async_advance_isr to clean up "REMOVING" queue head
- add helper find previous qhd
- add remove qhd from async list
- add is_removing field for async advance isr to clean up
add pipe close for control pipe & bulk pipe (with tests)
add helper get qhd from pipe_handle