rsi: Add host interface operations as separate structure.

Host interface operations are currently function pointers in rsi_hw
structure. As more host interface operations are going to be introduced,
separate structure is added for these for convenience.

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>