Azure RTOS 6.1.6

This is an updated release of Azure RTOS USBX that includes the following changes:

Files are modified to fixed build issues: 
    ux_device_class_storage_thread.c
    ux_host_class_storage_deactivate.c
    ux_hcd_ehci_interrupt_endpoint_create.c
    ux_hcd_ehci_interrupt_endpoint_destroy.c
    ux_hcd_ehci_isochronous_endpoint_create.c
    ux_hcd_ehci_isochronous_endpoint_destroy.c
    ux_hcd_ehci_least_traffic_list_get.c

Files are modified or added to refine device DFU, added DFU_UPLOAD support:
    ux_user_sample.h
    ux_api.h
    ux_device_class_dfu.h
    ux_device_class_dfu_activate.c
    ux_device_class_dfu_control_request.c
    ux_device_class_dfu_deactivate.c
    ux_device_class_dfu_initialize.c
    ux_device_class_dfu_state_get.c
    ux_device_class_dfu_state_sync.c

Files are modified to fixed device stack uninitialize issue:
    ux_device_stack_uninitialize.c

Files are modified to update DCD/HCD simulation for tests:
    ux_dcd_sim_slave.h
    ux_hcd_sim_host.h
    ux_dcd_sim_slave_initialize.c
    ux_dcd_sim_slave_initialize_complete.c
    ux_dcd_sim_slave_state_change.c
    ux_hcd_sim_host_initialize.c
    ux_hcd_sim_host_port_status_get.c
    ux_hcd_sim_host_transaction_schedule.c

Files are modified to add device audio volume RES support:
    ux_device_class_audio10.h
    ux_device_class_audio20.h
    ux_device_class_audio10_control_process.c
    ux_device_class_audio20_control_process.c

Files are modified to add device bi-directional-endpoints support:
    ux_dcd_sim_slave.h
    ux_dcd_sim_slave_endpoint_create.c
    ux_dcd_sim_slave_endpoint_status.c
    ux_device_stack_get_status.c
    ux_hcd_sim_host_transaction_schedule.c
    ux_user_sample.h