ARM: dts: omap3-gta04: give spi_lcd node a label so that we can overwrite in other DTS files

needed for device variants based on GTA04 board but with
different display panel (driver).

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