KVM: nVMX: Copy VMCS12 to processor-specific shadow vmcs

Introduce a function used to copy fields from the software controlled VMCS12
to the processor-specific shadow vmcs

Signed-off-by: Abel Gordon <abelg@il.ibm.com>
Reviewed-by: Orit Wasserman <owasserm@redhat.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>