hal_light: add permission to sys/class/leds.

/sys/class/leds is the standard location for linux files dealing with
leds, however the exact contents of this directory is non-standard
(hence the need for a hal).

Bug: 32022100
Test: compiles and works for the subset of common files
Change-Id: I7571d7267d5ed531c4cf95599d5f2acc22287ef4