powerpc/5200: Add Lite5200 on-board LEDs as devices

The Lite5200 evaluation board has a number of debug LEDs that Linux
doesn't know about yet. This change adds a gpio-leds stanza to the
lite5200 device tree so that the correct driver can get hooked up.

Also, make use of the dtc labels feature to reduce the number of source
lines required to add the gpio-controller property to the general
purpose timer nodes. In addition, the required #gpio-cells properties
are added to the common mpc5200b dtsi include file so that each board
doesn't need to add them explicitly. This still doesn't enable gpio
mode, 'gpio-controller' is required for that, but it means less work
needs to be done by board ports.

Cc: Anatolij Gustschin <agust@denx.de>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>