增加 gpiod_get_optional.

Signed-off-by: rick.chan <chenyang@autoai.com>

Software/Development/OperatingSystem/Linux/Kernel/API/Linux_Kernel_GPIO_API.md

@@ -101,7 +101,39 @@ flags：optional GPIO initialization flags。
 
 This is equivalent to gpiod_get_index(), except that when no GPIO with the specified index was assigned to the requested function it will return NULL。
 
-## 4. gpiod_direction_output 函数
+## 4. gpiod_get_optional 函数
+
+**头文件：**
+
+```cpp
+#include <linux/gpio/consumer.h>
+```
+
+**函数原型：**
+
+```cpp
+static inline struct gpio_desc *__must_check
+gpiod_get_optional(struct device *dev, const char *con_id,
+           enum gpiod_flags flags);
+```
+
+**说明：**
+
+Obtain an optional GPIO for a given GPIO function. This is equivalent to gpiod_get(), except that when no GPIO was assigned to the requested function it will return NULL. This is convenient for drivers that need to handle optional GPIOs.
+
+**参数：**
+
+dev：GPIO consumer, can be NULL for system-global GPIOs
+
+con_id：function within the GPIO consumer
+
+flags：optional GPIO initialization flags
+
+**返回值：**
+
+Equivalent to gpiod_get(), except that when no GPIO was assigned to the requested function it will return NULL.
+
+## 5. gpiod_direction_output 函数
 
 **头文件：**
 
@@ -129,7 +161,7 @@ value：initial output value of the GPIO。
 
 Return 0 in case of success, else an error code。
 
-## 5. gpiod_direction_input 函数
+## 6. gpiod_direction_input 函数
 
 **头文件：**
 
@@ -155,7 +187,7 @@ desc：GPIO to set to input。
 
 Return 0 in case of success, else an error code。
 
-## 6. gpiod_set_value_cansleep 函数
+## 7. gpiod_set_value_cansleep 函数
 
 **头文件：**