avocado/boot_linux_console.py: check for tcg in test_ppc_powernv8/9

avocado/boot_linux_console.py: check for tcg in test_ppc_powernv8/9

The PowerNV8/9 machines does not work with KVM acceleration, meaning
that boot_linux_console.py:BootLinuxConsole.test_ppc_powernv8/9 tests
will always fail when QEMU is compiled with --disable-tcg:

ERROR 1-tests/avocado/boot_linux_console.py:BootLinuxConsole.test_ppc_powernv8
-> VMLaunchFailure: ConnectError: Failed to establish session:
[Errno 104] Connection reset by peer
        Exit code: 1
        Command: ./qemu-system-ppc64 -display none -vga none -chardev socket,id=mon,path=/var/tmp/avo_qemu_sock_no19zg0m/qemu-1936936-7fffa77cff98-monitor.sock -mon chardev=mon,mode=control -machine powernv8 -chardev socket,id=console,path=/var/tmp/avo_qemu_sock_no19zg0m/qemu-1936936-7fffa77cff98-console.sock,server=on,wait=off -serial chardev:console -kernel /home/danielhb/avocado/data/cache/by_location/4514304e2c4ee84c5f0b5c8bacedda783891df68/zImage.epapr -append console=tty0 console=hvc0 -device pcie-pci-bridge,id=bridge1,bus=pcie.1,addr=0x0 -device nvme,bus=pcie.2,addr=0x0,serial=1234 -device e1000e,bus=bridge1,addr=0x3 -device nec-usb-xhci,bus=bridge1,addr=0x2
        Output: qemu-system-ppc64: The powernv machine does not work with KVM acceleration

Let's add the TCG accel requirement in both tests to skip them if we
don't have TCG support available.

Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20220303153517.168943-4-danielhb413@gmail.com>
Signed-off-by: Cédric Le Goater <clg@kaod.org>