KVM: X86: Store L1's TSC scaling ratio in 'struct kvm_vcpu_arch'

Store L1's scaling ratio in the kvm_vcpu_arch struct like we already do
for L1's TSC offset. This allows for easy save/restore when we enter and
then exit the nested guest.

Signed-off-by: Ilias Stamatis <ilstam@amazon.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20210526184418.28881-3-ilstam@amazon.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>