platform/x86: Fix run-time dependencies of OLPC drivers

Let the xo15-ebook driver depend on OLPC as all other OLPC drivers
already do. Add COMPILE_TEST as an alternative for both xo1-rfkill
and xo15-ebook, to increase the build testing coverage.

Signed-off-by: Jean Delvare <jdelvare@suse.de>
Cc: Matthew Garrett <matthew.garrett@nebula.com>
Signed-off-by: Matthew Garrett <matthew.garrett@nebula.com>