rtl8723au_bt: Update driver

On September 4, Realtek sent a new copy of the BlueTooth driver. This version
is intended to be a replacement for the existing kernel driver, thus the name
of the source is changed from rtk_btusb.c to btusb.c.

Although I have not looked into this code in detail, I did notice that the
firmware has been simplified as the driver no longer uses the *-config files.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
rtl8723au_bt: Update Makefile for alternate firmware names

There is some confusion as th whether the firmware shoule be names
xxxx_fw.bin or xxxx_fw. This change adds both forms to /lib/firmware.

With this change, a BT mouse works with my RTL8723AE device.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>