ARM: dts: gta04: improve panel compatibility string

Official vendor string is now "tpo" and not "toppoly".

Requires patch "omapdrm: panel: fix compatible vendor string for td028ttec1"
so that the driver understands both.

Signed-off-by: H. Nikolaus Schaller <hns@goldelico.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>