wifi: rtl8xxxu: Add LED control code for RTL8192EU

By default the LED will blink when there is some activity.

This was tested with a cheap "HT-WR813" from Aliexpress.

Signed-off-by: Bitterblue Smith <rtl8821cerfe2@gmail.com>
Reviewed-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/8f7fd5d7-5baa-b38b-ad2a-977dcd9edd81@gmail.com