Add missing flash device feature to the K82F board

Author: David Saada

targets/targets.json

@@ -691,7 +691,7 @@
         "macros": ["CPU_MK82FN256VDC15", "FSL_RTOS_MBED"],
         "inherits": ["Target"],
         "detect_code": ["0217"],
-        "device_has": ["ANALOGIN", "ANALOGOUT", "I2C", "I2CSLAVE", "INTERRUPTIN", "LOWPOWERTIMER", "PORTIN", "PORTINOUT", "PORTOUT", "PWMOUT", "RTC", "SERIAL", "SLEEP", "SPI", "SPISLAVE", "STDIO_MESSAGES", "TRNG"],
+        "device_has": ["ANALOGIN", "ANALOGOUT", "I2C", "I2CSLAVE", "INTERRUPTIN", "LOWPOWERTIMER", "PORTIN", "PORTINOUT", "PORTOUT", "PWMOUT", "RTC", "SERIAL", "SLEEP", "SPI", "SPISLAVE", "STDIO_MESSAGES", "TRNG", "FLASH"],
         "release_versions": ["2", "5"],
         "device_name": "MK82FN256xxx15"
     },