Use front LED as DISK LED by default

configname: CONFIG_ADB_PMU_LED_DISK

Linux Kernel Configuration
└─>Device Drivers
└─>Macintosh device drivers
└─>Use front LED as DISK LED by default
In linux kernel since version 4.1 (release Date: 2015-06-21)  
This option makes the front LED default to the disk trigger
so that it blinks on disk activity.