xhci: add helper to get the endpoint state of a endpoint context

define GET_EP_CTX_STATE() macro to get the endpoint state from a
pointer to a le32 enpoint context structure

No functional changes

Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>