wifi: rtw89: rewrite decision on channel by entity state

We need to invoke the callback of the changed band at the first
set_channel() after every power-off. Originally, we forced the
channel to be 0 when doing power-off, and then determined things
by comparing channel with 0.

However, deciding on such things by channel might be confusing.
It's also confusing to use this kind of decision when we consider
multiple channels in the follow-up patches. So, another flag,
entity_active, is added ahead to HAL to deal with this.

Besides, we also need to check if entity is active when we set
TX power.

Signed-off-by: Zong-Zhe Yang <kevin_yang@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20220809104952.61355-2-pkshih@realtek.com