KVM: selftests: Get rid of kvm_util_internal.h

Fold kvm_util_internal.h into kvm_util_base.h, i.e. make all KVM utility
stuff "public".  Hiding struct implementations from tests has been a
massive failure, as it has led to pointless and poorly named wrappers,
unnecessarily opaque code, etc...

Not to mention that the approach was a complete failure as evidenced by
the non-zero number of tests that were including kvm_util_internal.h.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>