init: Fix queue_all_property_triggers with nonexistent properties

Don't queue actions for "on property=*" if the property does not exist.
This fixes these errors on boot:

    init: property 'sys.powerctl' doesn't exist while
    expanding '${sys.powerctl}'
    init: powerctl: cannot expand '${sys.powerctl}

Change-Id: I3bd354d73a860f856be5df2c654f940445f9efd9
unpackbootimg: Add support for detecting lz4 compressed ramdisks

This will check for lz4 magic, and if found change the extension of the
file. Else it'll fall back to the default behavior of assuming gzip. This has
been tested with stock LS980 boot images and LS970 boot images for lz4
and gzip respectively.

Change-Id: If2139ff172397b6db079ffb7ab9cb61897c38fb3
ueventd.rc: Change owner of graphics drivers to system

iWifi Display service needs permission to open these drivers.

Change-Id: I1d9e4ae372f09ecf4104888a9910d09903d892d1
(cherry picked from commit f087420bf5eada3017e107a3a8da4e74f683da18)
(cherry picked from commit 1b3f9226cd3ad681a0ef08038d874921ca62ee4c)
(cherry picked from commit 5b4becc1b814b0f9e96d4f3aaec380d74f4b0739)