RDA5991e BT init program

Based on the code from Orange PI 2G-IOT SDK

gcc bt_init.c -o bt_init
./bt_init
hciattach -s 921600 /dev/ttyS1 any 921600 flow

Issues:

• hciattach doesn't work with speed suggested by platform config (3000000)
• scan doesn't work
• discoverable mode doesn't work

TODO:

• add command line parameters processing for the UART baud rate
• add compatibility with other BT variants if necessary