feat(cam): add camera buffer alloc function

docs/en/api-reference/peripherals/camera_driver.rst

@@ -112,6 +112,8 @@ Camera controller driver can be implemented in one of following ways:
 
     If :cpp:type:`esp_cam_ctlr_lcd_cam_cfg_t` is specified, users can call :cpp:func:`esp_cam_new_lcd_cam_ctlr` to allocate and initialize a DVP camera controller handle. This function will return an DVP camera controller handle if it runs correctly. You can take following code as reference.
 
+    After calling :cpp:func:`esp_cam_new_dvp_ctlr`, you should allocate a camera buffer that meets the alignment constraints, or call :cpp:func:`esp_cam_ctlr_alloc_buffer` to automatically allocate.
+
     .. code:: c
 
         esp_cam_ctlr_handle_t cam_handle = NULL;

docs/zh_CN/api-reference/peripherals/camera_driver.rst

@@ -112,6 +112,8 @@
 
     如果指定了 :cpp:type:`esp_cam_ctlr_dvp_config_t` 中的配置，就可以调用 :cpp:func:`esp_cam_new_dvp_ctlr` 来分配和初始化 DVP 摄像头控制器句柄。如果函数运行正确，将返回一个 DVP 摄像头控制器句柄。请参考以下代码。
 
+    在调用 :cpp:func:`esp_cam_new_dvp_ctlr` 之后，需要分配符合对齐约束的摄像头缓冲区，或调用 :cpp:func:`esp_cam_ctlr_alloc_buffer` 来自动分配。
+
     .. code:: c
 
         esp_cam_ctlr_handle_t cam_handle = NULL;