usb: Add end-point stall APIs and flow control APIS

USB class drivers may need to offload some work from
upcall interrupt context to a background fiber. This
requires some way to defer taking more data from host
till the offloaded work completes. Two APIs are added to
achieve this.

Further USB class drivers sometimes need to set STALL condition
on end-points to signal errors to host.These too are
added.

Change-Id: Ic973522c3394e23d7f9c4c67affc0cd050afc20f
Signed-off-by: Jithu Joseph <jithu.joseph@intel.com>