objtool: Move struct objtool_file into arch-independent header

The objtool_file structure describes the files objtool works on,
is used by the check subcommand, and the check.h header is included
by the orc subcommands so it's presently used by all subcommands.

Since the structure will be useful in all subcommands besides check,
and some subcommands may not want to include check.h to get the
definition, split the structure out into a new header meant for use
by all objtool subcommands.

Signed-off-by: Matt Helsley <mhelsley@vmware.com>
Reviewed-by: Julien Thierry <jthierry@redhat.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>