Fix getStackPointer() to work in RISC-V and ARM mode (#2526)

Author: maxgerhardt

cores/rp2040/RP2040Support.h

@@ -289,7 +289,11 @@ class RP2040 {
 
     inline uint32_t getStackPointer() {
         uint32_t *sp;
+#if defined(__riscv)
+        asm volatile("mv %0, sp" : "=r"(sp));
+#else
         asm volatile("mov %0, sp" : "=r"(sp));
+#endif
         return (uint32_t)sp;
     }