input: Write a python function to find the maximum value in a 2D list.
  assert find_max_val([[1, 4, 8], [7, 9, 6]]) == 9
  assert find_max_val([[0, -1, -3], [5, 2, 11], [4, 9, 7]]) == 11
  assert find_max_val([[3, 3, 3], [3, 3, 3], [3, 3, 3]]) == 3
output: def find_max_val(matrix):
      max_val = float('-inf')
      for row in matrix:
          for val in row:
              if val > max_val:
                  max_val = val
      return max_val