rsi: handle BT traffic in driver

BT frames are passed through coex and hal modules to BUS.
After firmware is loaded, based on the operating mode CARD
READY frame comes for each protocol. When BT card ready is
received, BT attach is called.
Protocol operations are exchanged between the modules
at initialization time.
Build flag CONFIG_RSI_COEX is introduced to enable coex support
if CONFIG_BT_RSIHCI is enabled. Coex operations are valid if
coex mode is greater than 1 only.

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