msm-fb-refresher: use *.files method to simplify code

Created by: ollieparanoid

Since it's possible to specify hook-specific binaries (see the debug-shell hook) that will be added to the initramfs, we can do the following:

• Install a hook with msm-fb-refresher, that will add the binary to the initramfs
• Remove the extra code from mkinitfs.sh that used deviceinfo_msm_refersher to do the same thing
• Remove the deviceinfo_msm_refresher variable