libelf: Do not read past end of buffer

Previously a corrupt ELF file could read beyond the end of e_rawfile.

Upstream elftoolchain ticket 462.  Found via the security/afl fuzzer.

Sponsored by:	The FreeBSD Foundation
- No longer exclude malo(4) and mwl(4), they have been fixed in r275870
  and r275871 respectively to build with PAE enabled.
- For the PAE kernel configuration file, no longer exclude devices that
  are known to be 64-bit DMA clean from amd64.

MFC after:	3 days