ARM: shmobile: lager: Use keyboard as gpio-keys node name

This appears to be the best match for ePAPR.
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>

arch/arm/boot/dts/r8a7790-lager.dts

@@ -43,7 +43,7 @@ lbsc {
 		#size-cells = <1>;
 	};
 
-	gpio_keys {
+	keyboard {
 		compatible = "gpio-keys";
 
 		button@1 {