selftests/nolibc: add configurations for riscv32

nolibc already supports riscv32. Wire it up in the testsuite.

Link: https://lore.kernel.org/r/20241221-nolibc-rv32-v1-6-d9ef6dab7c63@weissschuh.net


Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>