This function solves the problem (这个功能解决的问题)
hide the upload button when the number of file limit is reached, or disabled the upload button when the number of file limit is reached
Expected API (期望的 API)
<n-upload :max="2" list-type="image-card" /> // will hide the upload button when the number of file limit is reached.
<n-upload :disabled="fileList >=2" list-type="image-card" /> // will disabled the upload button when the number of file limit is reached.