KVM: VMX: Define a VMX glue macro for kvm_complete_insn_gp()

KVM: VMX: Define a VMX glue macro for kvm_complete_insn_gp()

Define kvm_complete_insn_gp() as vmx_complete_emulated_msr() and use the
glue wrapper in vt_complete_emulated_msr() so that VT's
.complete_emulated_msr() implementation follows the soon-to-be-standard
pattern of:

    vt_abc:
        if (is_td())
            return tdx_abc();
        return vmx_abc();

This will allow generating such wrappers via a macro, which in turn will
make it trivially easy to skip the wrappers entirely when KVM_INTEL_TDX=n.

Suggested-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/kvm/Z6v9yjWLNTU6X90d@google.com/
Cc: Sean Christopherson <seanjc@google.com>
Cc: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
Link: https://lore.kernel.org/r/20250318-vverma7-cleanup_x86_ops-v2-3-701e82d6b779@intel.com
[sean: massage shortlog+changelog]
Signed-off-by: Sean Christopherson <seanjc@google.com>