wifi: rtl8xxxu: Declare AP mode support for 8188f

Everything is in place now for AP mode, we can tell the system that we
support it. Put the feature behind a flag in priv->fops, because it is
not (yet) implemented for all chips.

Signed-off-by: Martin Kaistra <martin.kaistra@linutronix.de>
Reviewed-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230428150833.218605-18-martin.kaistra@linutronix.de