ddb ps: Print again the effective GID, separately

Following commit be1f7435ef218b1d ("kern: start tracking cr_gid outside
of cr_groups[]"), cr_groups[] doesn't contain the effective GID anymore.
Fix the 'show proc' DDB command to show it again, and make it stand out
with respect to the supplementary ones.

Fixes: be1f7435ef218b1d ("kern: start tracking cr_gid outside of cr_groups[]")
MFC after: 9 days
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D52251

(cherry picked from commit de974a0f1b73e79466c25f3c85fe727004576fea)