[ath_hal] extend the TX/RX descriptor layout to include location/beamforming fields.

• extend the TX timestamp to 32 bits, as the AR5416 and later does a full 32 bit TX timestamp instead of 15 or 16 bits.
• add RX descriptor fields for PHY uploaded information (coming soon)
• add flags for RX/TX fast timestamp, hardware upload, etc
• add a flag for TX to request ToD/ToA location information.