KVM: nSVM: Split off common definitions for Hyper-V on KVM and KVM on Hyper-V

In preparation to implementing Enlightened MSR-Bitmap feature for Hyper-V
on KVM, split off the required definitions into common 'svm/hyperv.h'
header.

No functional change intended.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20220202095100.129834-4-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>