mkbootimg: Add --dt parameter to specify DT image

New optional --dt parameter to specify a kernel device
tree image.

Change-Id: I7e2c48c25c04165642eedadc3dc16a082dd99eb0
ueventd: allow platform devices to have just a /devices/ prefix - DO NOT MERGE

When using device tree, platform devices may not have a
/devices/platform/ path prefix, but can be rooted in
/devices/.

Modify the platform device tracking code to store the device
path as well as the name. This way, when we create symlinks, we
can correctly skip the base platform device prefix and get to the
proper device node path.

Change-Id: I939ef8fbcb45c5c803cd9a054e40136a912efc72
Signed-off-by: Dima Zavin <dima@android.com>