tests/qtest/bios-tables-test: Only run VIOT test on TCG

The VIOT test does not always work under KVM on the virt machine:

  PASS 5 qtest-aarch64/bios-tables-test /aarch64/acpi/virt/oem-fields
  qemu-system-aarch64: kvm_init_vcpu: kvm_arch_init_vcpu failed (0): Invalid argument
  Broken pipe

Make it TCG only.

Reported-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

tests/qtest/bios-tables-test.c

@@ -1489,6 +1489,7 @@ static void test_acpi_virt_viot(void)
 {
     test_data data = {
         .machine = "virt",
+        .tcg_only = true,
         .uefi_fl1 = "pc-bios/edk2-aarch64-code.fd",
         .uefi_fl2 = "pc-bios/edk2-arm-vars.fd",
         .cd = "tests/data/uefi-boot-images/bios-tables-test.aarch64.iso.qcow2",