wifi: rtl8xxxu: Support new chip RTL8188EU

This chip is found in cheap USB devices from TP-Link, D-Link, etc.

Features: 2.4 GHz, b/g/n mode, 1T1R, 150 Mbps.

Chip versions older than "I cut" need software rate control. That will
be in the next commit. Until then MCS7 is used for all data frames.

The "I cut" chips are not supported. They require different firmware
and initialisation tables. Support can be added if someone has the
hardware to test it.

Co-developed-by: Andrea Merello <andrea.merello@gmail.com>
Signed-off-by: Andrea Merello <andrea.merello@gmail.com>
Co-developed-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: Jes Sorensen <Jes.Sorensen@gmail.com>
Co-developed-by: Bitterblue Smith <rtl8821cerfe2@gmail.com>
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/3aad60f6-23f9-81e8-c741-4bd51e99f423@gmail.com