KVM: TDX: Fold tdx_bringup() into tdx_hardware_setup()

KVM: TDX: Fold tdx_bringup() into tdx_hardware_setup()

Now that TDX doesn't need to manually enable virtualization through _KVM_
APIs during setup, fold tdx_bringup() into tdx_hardware_setup() where the
code belongs, e.g. so that KVM doesn't leave the S-EPT kvm_x86_ops wired
up when TDX is disabled.

The weird ordering (and naming) was necessary to allow KVM TDX to use
kvm_enable_virtualization(), which in turn had a hard dependency on
kvm_x86_ops.enable_virtualization_cpu and thus kvm_x86_vendor_init().

Tested-by: Chao Gao <chao.gao@intel.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Tested-by: Sagi Shahar <sagis@google.com>
Link: https://patch.msgid.link/20260214012702.2368778-17-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>