Header frame.h is getting more code annotations to help objtool analyze
object files.

Rename the file to objtool.h.

[ jpoimboe: add objtool.h to MAINTAINERS ]
Signed-off-by: NJulien Thierry <jthierry@redhat.com>
Signed-off-by: NJosh Poimboeuf <jpoimboe@redhat.com>