avocado/boot_linux_console.py: check TCG accel in test_ppc_mac99()

This test breaks when run in an IBM POWER host with a QEMU compiled
with --disable-tcg and the ppc-softmmu target in a similar manner as
test_ppc_g3beige did.

There's also an observation made about kvm_pr in the error message:

Command: ./qemu-system-ppc -display none -vga none (...)
-machine mac99 (...)
        Output: ioctl(KVM_CREATE_VM) failed: 22 Invalid argument
PPC KVM module is not loaded. Try modprobe kvm_pr.
qemu-system-ppc: failed to initialize kvm: Invalid argument

This means that, when/if we're able to detect kvm_pr support in these
avocado tests, we can revisit this test to not rely solely on TCG
availability.

Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Message-Id: <20220310183011.110391-3-danielhb413@gmail.com>
Signed-off-by: Cédric Le Goater <clg@kaod.org>

tests/avocado/boot_linux_console.py

@@ -1228,7 +1228,13 @@ class BootLinuxConsole(LinuxKernelTest):
         """
         :avocado: tags=arch:ppc
         :avocado: tags=machine:mac99
+        :avocado: tags=accel:tcg
         """
+        # TODO: mac99 works with kvm_pr but we don't have a
+        # reliable way ATM (e.g. looking at /proc/modules) to detect
+        # whether we're running kvm_hv or kvm_pr. For now let's
+        # disable this test if we don't have TCG support.
+        self.require_accelerator("tcg")
         tar_hash = 'e0b872a5eb8fdc5bed19bd43ffe863900ebcedfc'
         self.vm.add_args('-M', 'graphics=off')
         self.do_test_advcal_2018('15', tar_hash, 'invaders.elf')