bi_load: only add MODULEP on arches that have it defined

Do not attempt to add MODINFOMD_MODULEP to the kernel medatada on
arches that don't have it defined.

This fixes the build for arches different than amd64 after
7d3259775cb69f250df3e7fe51d6fff2283c6f20.

Sponsored by: Citrix Systems R&D
Reported by: lwhsu, arichardson