dtoverlays: Make piscreen consistent on swapxy

The overlay had the TI proprietary "ti,swap-xy" defined by default,
but the override for swapxy then used the generic "touchscreen-swapped-x-y"

Swap the default to use "touchscreen-swapped-x-y" to make the configuration
consistent.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>

Author: 6by9

arch/arm/boot/dts/overlays/piscreen-overlay.dts

@@ -88,7 +88,7 @@
 				interrupts = <17 2>; /* high-to-low edge triggered */
 				interrupt-parent = <&gpio>;
 				pendown-gpio = <&gpio 17 GPIO_ACTIVE_LOW>;
-				ti,swap-xy;
+				touchscreen-swapped-x-y;
 				ti,x-plate-ohms = /bits/ 16 <100>;
 				ti,pressure-max = /bits/ 16 <255>;
 			};