driver: Use hypervisor's version.h

Let the driver module depend on the hypervisor subdir. This allows us to
reuse the version.h generated by the hypervisor build also for the
driver. They were identical.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
core: config.h is expected in the $(obj), not $(src)

Cosmetic change, both are identical in practice (no out-of-tree build
possible for out-of-tree modules right now).

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>