What:		/sys/class/chromeos/<ec-device-name>/pd_update/firmware_images
Date:		August 2015
KernelVersion:	4.2
Description:
		List the names of the available firmware images for USB PD
    that use cros_ec OS.
    Each line contains a slot, PD major/minor and firmware name:
    0: 1.1 cros-pd/zinger_v1.7.539-91a0fa2.bin

    The images are in the kernel firmware images directory.