ivshmem-test.c: enable test_ivshmem_server for ppc64 arch

ivshmem-test.c: enable test_ivshmem_server for ppc64 arch

This test, if enabled by hand, was failing when the ivhsmem device was
being declared as DEVICE_NATIVE_ENDIAN with the following error:

/ppc64/ivshmem/pair: OK
/ppc64/ivshmem/server:
**
ERROR:/home/danielhb/qemu/tests/qtest/ivshmem-test.c:367:test_ivshmem_server:
assertion failed (ret != 0): (0 != 0)
Aborted

After the endianness change done in the previous patch, we can verify in
both a a Power 9 little-endian host and in a Power 8 big-endian host
that this test is now passing:

$ QTEST_QEMU_BINARY=./ppc64-softmmu/qemu-system-ppc64 ./tests/qtest/ivshmem-test -m slow
/ppc64/ivshmem/single: OK
/ppc64/ivshmem/hotplug: OK
/ppc64/ivshmem/memdev: OK
/ppc64/ivshmem/pair: OK
/ppc64/ivshmem/server: OK

Let's keep it that way by officially enabling it for ppc64.

Acked-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20211124092948.335389-3-danielhb413@gmail.com>
Signed-off-by: Cédric Le Goater <clg@kaod.org>