OBI protocol hardening

Created by: silabs-oysteink

Added OBI protocol hardening. A major alert will be flagged if any OBI interface receive an _rvalid when the outstanding counter is zero. A similar check is performed in the LSU on the inside of the MPU, also resulting in alert_major if the MPU sends a valid response when the outstanding counter int he LSU is zero.

Not SEC clean as this fans into changes in alert_major_o.

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