Cherry picked commit for addition of Smstateen CSRs from CV32E40X.

Created by: silabs-oysteink

Added fence.i related notes. Added mstateen CSRs (applicable to CV32E40S, not to CV32E40X)

Signed-off-by: Arjan Bink Arjan.Bink@silabs.com Signed-off-by: Oystein Knauserud Oystein.Knauserud@silabs.com