agp: Fix up email address & attributions in AGP MODULE_AUTHOR tags

- Remove soon-to-be-dead @redhat address.
- Jeff Hartmann wrote the bulk of the original backend code, and should
  at least get a mention in the MODULE_AUTHOR for backend.o
- Various people at Intel have done a lot more work than myself on the
  intel-* drivers, so again, mention that.

Signed-off-by: Dave Jones <davej@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>