renamed and extended GTA04 specific beagle board configs

Signed-off-by: H. Nikolaus Schaller <hns@goldelico.com>
added plain GTA04 Beagleboard variant (no expander)

Signed-off-by: H. Nikolaus Schaller <hns@goldelico.com>
added GTA04 Beagleboard variant with b7 expander (Neo900)

Signed-off-by: H. Nikolaus Schaller <hns@goldelico.com>
fixed compile issues for the BB variants

Signed-off-by: H. Nikolaus Schaller <hns@goldelico.com>
added some menu and splash images

Signed-off-by: H. Nikolaus Schaller <hns@goldelico.com>
removed some printenv commands to reduce the boot log

Signed-off-by: H. Nikolaus Schaller <hns@goldelico.com>