KVM: x86/mmu: Reject direct bits in gpa passed to KVM_PRE_FAULT_MEMORY

Only let userspace pass the same addresses that were used in KVM_SET_USER_MEMORY_REGION
(or KVM_SET_USER_MEMORY_REGION2); gpas in the the upper half of the address space
are an implementation detail of TDX and KVM.

Extracted from a patch by Sean Christopherson <seanjc@google.com>.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>