allow doxygen to generate documentation for SAI peripheral

Author: ithinuel

doxyfile_options

@@ -2090,6 +2090,7 @@ PREDEFINED             = DOXYGEN_ONLY            \
                          DEVICE_SERIAL_ASYNCH    \
                          DEVICE_SERIAL_FC        \
                          DEVICE_SLEEP            \
+                         DEVICE_SAI              \
                          DEVICE_SPI              \
                          DEVICE_SPI_ASYNCH       \
                          DEVICE_SPISLAVE         \

doxygen_options.json

@@ -6,7 +6,7 @@
     "SEARCH_INCLUDES": "YES",
     "INCLUDE_PATH": "", 
     "INCLUDE_FILE_PATTERNS": "", 
-    "PREDEFINED": "DOXYGEN_ONLY DEVICE_ANALOGIN DEVICE_ANALOGOUT DEVICE_CAN DEVICE_CRC DEVICE_ETHERNET DEVICE_EMAC DEVICE_FLASH  DEVICE_I2C DEVICE_I2CSLAVE DEVICE_I2C_ASYNCH DEVICE_INTERRUPTIN DEVICE_ITM DEVICE_LPTICKER DEVICE_PORTIN DEVICE_PORTINOUT DEVICE_PORTOUT DEVICE_PWMOUT DEVICE_RTC DEVICE_TRNG DEVICE_SERIAL DEVICE_SERIAL_ASYNCH DEVICE_SERIAL_FC DEVICE_SLEEP DEVICE_SPI DEVICE_SPI_ASYNCH DEVICE_SPISLAVE DEVICE_STORAGE \"MBED_DEPRECATED_SINCE(f, g)=\" \"MBED_ENABLE_IF_CALLBACK_COMPATIBLE(F, M)=\" \"MBED_DEPRECATED(s)=\"",
+    "PREDEFINED": "DOXYGEN_ONLY DEVICE_ANALOGIN DEVICE_ANALOGOUT DEVICE_CAN DEVICE_CRC DEVICE_ETHERNET DEVICE_EMAC DEVICE_FLASH DEVICE_SAI DEVICE_I2C DEVICE_I2CSLAVE DEVICE_I2C_ASYNCH DEVICE_INTERRUPTIN DEVICE_ITM DEVICE_LPTICKER DEVICE_PORTIN DEVICE_PORTINOUT DEVICE_PORTOUT DEVICE_PWMOUT DEVICE_RTC DEVICE_TRNG DEVICE_SERIAL DEVICE_SERIAL_ASYNCH DEVICE_SERIAL_FC DEVICE_SLEEP DEVICE_SPI DEVICE_SPI_ASYNCH DEVICE_SPISLAVE DEVICE_STORAGE \"MBED_DEPRECATED_SINCE(f, g)=\" \"MBED_ENABLE_IF_CALLBACK_COMPATIBLE(F, M)=\" \"MBED_DEPRECATED(s)=\"",
     "EXPAND_AS_DEFINED": "", 
     "SKIP_FUNCTION_MACROS": "NO",
     "STRIP_CODE_COMMENTS": "NO",