These timer registers are all 1uS in resolution in AR5416 or later. Previous hardware had some as TU, some as 1/8th TU.
These timer registers are all 1uS in resolution in AR5416
or later. Previous hardware had some as TU, some as 1/8th
TU.

* Modify AR_NEXT_DBA and AR_NEXT_SWBA to use a new macro,
  ONE_EIGHTH_TU_TO_USEC(), which converts the 1/8th TU
  fields to USEC. This is just cosmetic and matches the
  Atheros reference driver.

* Fix AR_NEXT_TBTT, which is USEC, not TU.

Submitted by:	paradyse@gmail.com
Approved by:	re (kib, blanket)

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase