#98 SOA messages support for psp 103.6 models needed

[Patrick Fath]

SOA messages support for psp 103.6 models needed (already implemented in VBIC model e.g.)
The following statements (from the manual) do not hold for the PSP 103.6 models of mosfets.
Vgs_max: If |Vgs| exceeds Vgs_max, SOA warning is issued.
Vgd_max: If |Vgd| exceeds Vgd_max, SOA warning is issued.
Vgb_max: If |Vgb| exceeds Vgb_max, SOA warning is issued.
Vds_max: If |Vds| exceeds Vds_max, SOA warning is issued.
Vbs_max: If |Vbs| exceeds Vbs_max, SOA warning is issued.
Vbd_max: If |Vbd| exceeds Vbd_max, SOA warning is issued.

[Patrick Fath]

In addition, I could not find the implementation of the SOA messages support for the VBIC models in https://github.com/dwarning/VA-Models/, maybe it's added in ngspice somewhere? If you give me the location i can try to add the feature also to the PSP implementation.

[Dietmar Warning]

SOA checks are implemented in the ngspice built-in VBIC model. AFAIK it is not in the VA version and also not for other VA models.
The manual describe the implemented version for BSIM3 and 4 built-in models.
It is to consider that the checks will downgrade the run time performance.

[Dietmar Warning]

There is a PR https://github.com/IHP-GmbH/IHP-Open-PDK/pull/610
@p-fath could you please check it. Thanks.