rtw89: pci: use a struct to describe all registers address related to DMA channel

We have had a struct rtw89_pci_ch_dma_addr to describe register address,
so use it as regular. Since the addresses should be changed dynamically
according to operating mode, I don't change it to be constant.

These changes don't affect the logic, so I put them in this separated
patch.

Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20220307060457.56789-5-pkshih@realtek.com