kld: Reject kernel modules with PT_LOAD segments where filesz > memsz

All sorts of places in the ELF loading code assume that filesz <=
memsz, so check that explicitly up front.

Reported by: Jane Smith <thebugfixers@pm.me> (via D57785)
Reviewed by: jrtc27, kib
Differential Revision: https://reviews.freebsd.org/D58542