The initial position of the joints can be influenced using joint targets.
Those are set within the joint. Here is a screenshot of the Revolute Joint with the desired angle set to 180 deg.
You can check your assembly by opening the Simscape Variable Viewer.
Here is a screenshot showing that not all joints achieved their desired initial positions from model sm_double_wishbone_suspension
If you are modeling suspensions, you also should take a look at the Simscape Vehicle Templates. This is a free set of templates for modeling vehicle dynamics and vehicle powertrains in Simscape. You can see many animations on this page: