KVM: x86/tdx: Do VMXON and TDX-Module initialization during subsys init

KVM: x86/tdx: Do VMXON and TDX-Module initialization during subsys init

Now that VMXON can be done without bouncing through KVM, do TDX-Module
initialization during subsys init (specifically before module_init() so
that it runs before KVM when both are built-in).  Aside from the obvious
benefits of separating core TDX code from KVM, this will allow tagging a
pile of TDX functions and globals as being __init and __ro_after_init.

Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Chao Gao <chao.gao@intel.com>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Tested-by: Chao Gao <chao.gao@intel.com>
Tested-by: Sagi Shahar <sagis@google.com>
Link: https://patch.msgid.link/20260214012702.2368778-12-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>