arch: riscv: Add support for stack unwind without fp

Add a stack unwind implementation that only uses `sp`

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

tests/arch/common/stack_unwind/testcase.yaml

@@ -4,7 +4,7 @@ common:
   ignore_qemu_crash: true
   tags: kernel
 tests:
-  arch.common.stack_unwind.riscv:
+  arch.common.stack_unwind.riscv_fp:
     arch_allow: riscv
     integration_platforms:
       - qemu_riscv32
@@ -16,6 +16,17 @@ tests:
         - "E: call trace:"
         - "E:       0: fp: \\w+   ra: \\w+"
         - "E:       1: fp: \\w+   ra: \\w+"
+  arch.common.stack_unwind.riscv_sp:
+    arch_allow: riscv
+    integration_platforms:
+      - qemu_riscv32
+      - qemu_riscv64
+    harness_config:
+      type: multi_line
+      regex:
+        - "E: call trace:"
+        - "E:       0: sp: \\w+   ra: \\w+"
+        - "E:       1: sp: \\w+   ra: \\w+"
   arch.common.stack_unwind.x86:
     arch_allow: x86
     extra_configs: