KVM: VMX: Refresh list of user return MSRs after setting guest CPUID

After a CPUID update, refresh the list of user return MSRs that are
loaded into hardware when running the vCPU.  This is necessary to handle
the oddball case where userspace exposes X86_FEATURE_RDTSCP to the guest
after the vCPU is running.

Fixes: 0023ef39 ("kvm: vmx: Set IA32_TSC_AUX for legacy mode guests")
Fixes: 4e47c7a6 ("KVM: VMX: Add instruction rdtscp support for guest")
Reviewed-by: Reiji Watanabe <reijiw@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210713163324.627647-35-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>