insane: only load real files as ELF

insane: only load real files as ELF

The file path checks are passed an ELF object if the file is an ELF. It
doesn't make a lot of sense to load symlinks to ELFs as if they're in
the same package then the real file will be checked too.

This should speed up do_package_qa slightly as libraries won't be
scanned repeatedly.

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>