Implement argmax function

Completed the implementation of the `argmax` function. It scans
an integer array to find the maximum value and returns the
0-based index of its first occurrence.

Changes include:
- Implemented the main loop to iterate through the array.
- Updated maximum value (`t0`) and index (`t1`) when a larger
  element is found.
- Ensured the function terminates gracefully using the `end`
  label, with the result stored in `a0`.

Author: yy214123

src/argmax.s

@@ -31,6 +31,23 @@ argmax:
     li t2, 1
 loop_start:
     # TODO: Add your own implementation
+    bge t2, a1, end
+    
+    slli t3, t2, 2
+    add t4, a0, t3
+    lw t5, 0(t4)
+    
+    ble t5, t0, next_element #<= nochange
+    
+    mv t0, t5
+    mv t1, t2
+    
+next_element:
+    addi t2, t2, 1
+    j loop_start
+end:
+    mv a0, t1
+    jr ra
 
 handle_error:
     li a0, 36