rsi: add rx control block to handle rx packets in USB

Rx bluetooth endpoint shall be added in further patches. Rx control
block is introduced here to handle Rx packets properly. Separate
function is written to initialize the RX control blocks.

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