KVM: VMX: return early if msr_bitmap is not supported

KVM: VMX: return early if msr_bitmap is not supported

The vmx_msr_filter_changed() may directly/indirectly calls only
vmx_enable_intercept_for_msr() or vmx_disable_intercept_for_msr(). Those
two functions may exit immediately if !cpu_has_vmx_msr_bitmap().

vmx_msr_filter_changed()
-> vmx_disable_intercept_for_msr()
-> pt_update_intercept_for_msr()
   -> vmx_set_intercept_for_msr()
      -> vmx_enable_intercept_for_msr()
      -> vmx_disable_intercept_for_msr()

Therefore, we exit early if !cpu_has_vmx_msr_bitmap().

Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
Link: https://lore.kernel.org/r/20240223202104.3330974-3-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>