Bluetooth: btrsi: add new rsi bluetooth driver

Redpine bluetooth driver is a thin driver which depends on
'rsi_91x' driver for transmitting and receiving packets
to/from device. It creates hci interface when attach() is
called from 'rsi_91x' module.

Signed-off-by: Prameela Rani Garnepudi <prameela.j04cs@gmail.com>
Signed-off-by: Siva Rebbagondla <siva.rebbagondla@redpinesignals.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Reviewed-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Amitkumar Karwar <amit.karwar@redpinesignals.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>