wifi: rtl8xxxu: cleanup includes

Remove unnecessary includes from driver. The first step is to add
necessary includes to driver's header files to make them can be included
individually. Then, driver's C files include driver's header files first,
and check if still missed header files of kernel.

The results show that most C files only include driver's header files.
Only core.c needs to include additional linux/firmware.h.

Also sort includes in alphabetic order.

Compile tested only.

Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://msgid.link/20240429024711.30992-1-pkshih@realtek.com

wifi: rtl8xxxu: remove rtl8xxxu_ prefix from filenames

The driver is already in a directory named rtl8xxxu, there's no need to
duplicate that in the filename as well. Now file listing looks a lot more
reasonable:

8188e.c 8192c.c 8192f.c 8723a.c core.c Makefile rtl8xxxu.h
8188f.c 8192e.c 8710b.c 8723b.c Kconfig regs.h

No functional changes, compile tested only.

Signed-off-by: Kalle Valo <kvalo@kernel.org>
Reviewed-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://msgid.link/20240426141939.3881678-2-kvalo@kernel.org