XGC-220 case: reduced and constant contribution to the anomalous particle transport

The FMCFM interface is modified and particle diffusivity is updated for this case with tbl_d_coeff_in;:

fm_ion_diff_norm%particle(i) = tbl_d_coeff_in * fm_norm_diff

The particle diffusivity in the core region is selected to be 0.01 m^2/sec.