ath9k_hw: add a macro for abstracting generic timer access

#define AR_FIRST_NDP_TIMER                  7

#define AR_NDP2_PERIOD                      0x81a0

#define AR_NDP2_TIMER_MODE                  0x81c0

#define AR_NEXT_TBTT_TIMER                  0x8200

#define AR_NEXT_DMA_BEACON_ALERT            0x8204

#define AR_NEXT_SWBA                        0x8208

#define AR_NEXT_CFP                         0x8208

#define AR_NEXT_HCF                         0x820C

#define AR_NEXT_TIM                         0x8210

#define AR_NEXT_DTIM                        0x8214

#define AR_NEXT_QUIET_TIMER                 0x8218

#define AR_NEXT_NDP_TIMER                   0x821C

#define AR_BEACON_PERIOD                    0x8220

#define AR_DMA_BEACON_PERIOD                0x8224

#define AR_SWBA_PERIOD                      0x8228

#define AR_HCF_PERIOD                       0x822C

#define AR_TIM_PERIOD                       0x8230

#define AR_DTIM_PERIOD                      0x8234

#define AR_QUIET_PERIOD                     0x8238

#define AR_NDP_PERIOD                       0x823C

#define AR_GEN_TIMERS(_i)                   (0x8200 + ((_i) << 2))

#define AR_NEXT_TBTT_TIMER                  AR_GEN_TIMERS(0)

#define AR_NEXT_DMA_BEACON_ALERT            AR_GEN_TIMERS(1)

#define AR_NEXT_SWBA                        AR_GEN_TIMERS(2)

#define AR_NEXT_CFP                         AR_GEN_TIMERS(2)

#define AR_NEXT_HCF                         AR_GEN_TIMERS(3)

#define AR_NEXT_TIM                         AR_GEN_TIMERS(4)

#define AR_NEXT_DTIM                        AR_GEN_TIMERS(5)

#define AR_NEXT_QUIET_TIMER                 AR_GEN_TIMERS(6)

#define AR_NEXT_NDP_TIMER                   AR_GEN_TIMERS(7)

#define AR_BEACON_PERIOD                    AR_GEN_TIMERS(8)

#define AR_DMA_BEACON_PERIOD                AR_GEN_TIMERS(9)

#define AR_SWBA_PERIOD                      AR_GEN_TIMERS(10)

#define AR_HCF_PERIOD                       AR_GEN_TIMERS(11)

#define AR_TIM_PERIOD                       AR_GEN_TIMERS(12)

#define AR_DTIM_PERIOD                      AR_GEN_TIMERS(13)

#define AR_QUIET_PERIOD                     AR_GEN_TIMERS(14)

#define AR_NDP_PERIOD                       AR_GEN_TIMERS(15)

#define AR_TIMER_MODE                       0x8240

#define AR_TBTT_TIMER_EN                    0x00000001