Firstly, GRE scores are not accepted for the PGP MBA program. Only CAT/GMAT scores are accepted. To apply through the GMAT route you need sufficient work experience in a foreign country.
For the FPM program, like any other doctoral program, the quality of the application matters the most and there is no cut-off for the GRE scores. Other factors that are actually considered are
Profile
Past research
Publications
There is no specific GRE score that would guarantee a call-up from IIM Ahmedabad.