kunit: qemu_configs: Add riscv32 config

Add a basic config to run kunit tests on riscv32.

Link: https://lore.kernel.org/r/20250407-kunit-qemu-riscv32-v1-1-7b9800034a35@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>