board: ti: am57xx: use GPIO_TO_PIN() to define GPIO number

Using the macro makes code readable without the need for a comment.

Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
diff --git a/board/ti/am57xx/board.c b/board/ti/am57xx/board.c
index 8720eb8..c41aa24 100644
--- a/board/ti/am57xx/board.c
+++ b/board/ti/am57xx/board.c
@@ -68,8 +68,7 @@
 DECLARE_GLOBAL_DATA_PTR;
 
 #define GPIO_ETH_LCD		GPIO_TO_PIN(2, 22)
-/* GPIO 7_11 */
-#define GPIO_DDR_VTT_EN 203
+#define GPIO_DDR_VTT_EN		GPIO_TO_PIN(7, 11)
 
 /* Touch screen controller to identify the LCD */
 #define OSD_TS_FT_BUS_ADDRESS	0