wifi: rtl8xxxu: Enable AP mode for RTL8192CU (RTL8188CUS)

This allows the driver to be used in wireless access point mode on the
AT91SAM9G25-based GARDENA smart Gateway.

Unfortunately, the data throughput in AP mode appears to be lower than
with the vendor driver (or in STA mode). Especially when sending, the
data rate is significantly lower. My measurements performed with iperf3
and an Edimax EW-7811Un (VID: 7392, PID: 7811) showed a maximum TX rate
of about 4 Mbits/sec compared to the ~24 Mbits/sec measured with the
rtl8192cu driver.

Although the performance might be good enough for our use case, this is
something that should be further looked into.

Signed-off-by: Ezra Buehler <ezra.buehler@husqvarnagroup.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://patch.msgid.link/20250122071512.10165-1-ezra@easyb.ch