KVM: selftests: Use "standard" min virtual address for CPUID test alloc

Use KVM_UTIL_MIN_ADDR as the minimum for x86-64's CPUID array.  The
system page size was likely used as the minimum because _something_ had
to be provided.  Increasing the min from 0x1000 to 0x2000 should have no
meaningful impact on the test, and will allow changing vm_vaddr_alloc()
to use KVM_UTIL_MIN_VADDR as the default.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210622200529.3650424-11-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>