tests: arch: common: stack_unwind: add qemu_riscv32e

qemu_riscv32e uses a different ISA and is kinda special, add it
to the testcase for better coverage.

Signed-off-by: Yong Cong Sin <ycsin@meta.com>
Signed-off-by: Yong Cong Sin <yongcong.sin@gmail.com>