Merge branch 'kvm-tdx-finish-initial' into HEAD

This patch ties the remaining loose ends and finally enables TDX guests to
run inside KVM.  It implements handling of EPT violation/misconfig and of
several TDVMCALL leaves that are handled in the kernel (CPUID, HLT, RDMSR/WRMSR,
GetTdVmCallInfo); it also adds a bunch of wrappers in vmx/main.c to
ignore operations not supported by TDX guests(*)

Finally, it introduces documentation for the new APIs that have been
added along the way.

(*) access to CPU state, VMX preemption timer, accesses to TSC offset or
    multiplier, LMCE enable/disable, hypercall patching.