rsi: use enum for FSM states

Currently macros are used for FSM states. We will replace
it with enum so that new state can be added easily without
worrying about macro value.

Signed-off-by: Amitkumar Karwar <amit.karwar@redpinesignals.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>