Lin: enable MHK lin with warnings

There are pieces still missing for good MHK linearization:
- buoyancy is not included in the perturbations
- added mass is not included in AeroDyn at all

modules/openfast-library/src/FAST_Subs.f90

@@ -2271,7 +2271,7 @@ SUBROUTINE ValidateInputData(p, m_FAST, ErrStat, ErrMsg)
 
    IF (p%MHK /= MHK_None .and. p%MHK /= MHK_FixedBottom .and. p%MHK /= MHK_Floating) CALL SetErrStat( ErrID_Fatal, 'MHK switch is invalid. Set MHK to 0, 1, or 2 in the FAST input file.', ErrStat, ErrMsg, RoutineName )
 
-   IF (p%MHK /= MHK_None .and. p%Linearize) CALL SetErrStat( ErrID_Fatal, 'Linearization has not yet been implemented for an MHK turbine. Change MHK or Linearize in the FAST input file.', ErrStat, ErrMsg, RoutineName )
+   IF (p%MHK /= MHK_None .and. p%Linearize) CALL SetErrStat( ErrID_Warn, 'Linearization is not fully implemented for an MHK turbine (buoyancy not included in perturbations, and added mass not included anywhere).', ErrStat, ErrMsg, RoutineName )
 
    IF (p%Gravity < 0.0_ReKi) CALL SetErrStat( ErrID_Fatal, 'Gravity must not be negative.', ErrStat, ErrMsg, RoutineName )