Start the process of migrating the ANI statistics out of the HALs and into
the top-level HAL.

The athstats program is blindly using a copy of the ar5212 ANI stats structure
to pull out ANI statistics/state and this is problematic for the AR9300
HAL.

So:

• Define HAL_ANI_STATS and HAL_ANI_STATE
• Use HAL_ANI_STATS inside the AR5212 HAL

This commit doesn't (yet) convert the ar5212AniState -> HAL_ANI_STATE when
exporting it to userland; that'll come in the next commit.