usb: xhci: merge xhci_queue_bulk_tx and queue_bulk_sg_tx functions

In drivers/usb/host/xhci-ring.c there are two functions
(xhci_queue_bulk_tx and queue_bulk_sg_tx) that are very similar,
so a lot of code duplication.
This patch merges these functions into to one xhci_queue_bulk_tx.
Also counting the needed TRBs is merged and refactored.

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