kvm: move all s390 ioctls inside ifdef

[bonzini]

Linux 6.9 cleaned up some of the struct definitions for architecture-specific KVM ioctls, moving them to the headers for that architecture in asm/. However, the result is that ioctls are defined but not usable. This can be fixed upstream, but is it worth it? There are actually a lot of other cases where the ioctls were placed in linux/kvm.h (to avoid numbering conflicts) but the struct is only defined for specific architectures, so place these s390-specific ioctls in the same group.

[kernelslacker]

Merged pull request #48 which should fix this.