kunit: qemu_configs: Add 64-bit SPARC configuration

Add a basic config to run kunit tests on 64-bit SPARC.

Link: https://lore.kernel.org/r/20250415-kunit-qemu-sparc64-v1-2-253906f61102@linutronix.de


Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Reviewed-by: David Gow <davidgow@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>