wifi: rtl8xxxu: Add central frequency offset tracking

According to Realtek programmers, "to adjust oscillator to align
central frequency of connected AP. Then, it can yield better
performance." From commit fb8517f4 ("rtw88: 8822c: add CFO
tracking").

The RTL8192CU and a version of RTL8723AU apparently don't have the
ability to adjust the oscillator, so this doesn't apply to them.

This also doesn't apply to the wifi + bluetooth combo chips (RTL8723AU
and RTL8723BU) because the CFO tracking should only be done when
bluetooth is disabled, and determining that looked complicated.

That leaves only the RTL8192EU and RTL8188FU chips. I tested this with
the latter.

Signed-off-by: Bitterblue Smith <rtl8821cerfe2@gmail.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/80aba428-0aff-f4b2-dea5-35d1425982b6@gmail.com