rsi: add coex support

With BT support, driver has to handle two streams of data
(i.e. wlan and BT). Actual coex implementation is in firmware.
Coex module just schedule the packets to firmware by taking them
from the corresponding paths.

Structures for module and protocol operations are introduced for
this purpose. Protocol operations structure is global structure
which can be shared among different modules. Move initialization
of coex and operating mode values to rsi_91x_init().

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>