- Fix Tx queues to USB endpoints mapping and merge urtwn_r92c_dma_init()

- Fix Tx queues to USB endpoints mapping and merge urtwn_r92c_dma_init()
  and urtwn_r88e_dma_init() into one; from FreeBSD r291902.

- Change the way the number of pages for public queue is calculated;
  Based on the vendor driver's _InitQueueReservedPage(), the formula for
  calculation of the number of pages for public priority queue is as follows:

  if the device has 3 endpoints:
  PUBQ = total number of Tx pages - HQ - LQ - NQ

  if the device has 2 endpoints (i.e. has high and normal priority queues):
  PUBQ = total number of Tx pages - HQ - NQ

- Don't write MCS8..MCS15 Tx power if the WNIC is a 1-stream Tx;

- Set R88E_TX_PAGE_COUNT to a correct value;

- Minimal enhancement in urtwn_open_pipes() for upcoming rtl8192eu chipset
  support;

Tested with USB-N10 Nano (rtl8188cu), DWA-131 rev B (rtl8192cu), and
TL-WN725N v2 (rtl8188eu) on amd64.

ok stsp@