at91: fix devicetree warnings

This commit fixes various devicetree warnings in the at91 devicetrees
like:
arch/arm/dts/sama5d36ek_cmp.dtb: Warning (avoid_unnecessary_addr_size): /gpio_keys: unnecessary #address-cells/#size-cells without "ranges" or child "reg" property

These warnings make buildman report failed builds for most of at91 boards.
Thus, fixing it.

Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>
diff --git a/arch/arm/dts/at91-vinco.dts b/arch/arm/dts/at91-vinco.dts
index ff6d2e3..0ecb64e 100644
--- a/arch/arm/dts/at91-vinco.dts
+++ b/arch/arm/dts/at91-vinco.dts
@@ -152,6 +152,8 @@
 			};
 
 			tcb2: timer@fc024000 {
+				#address-cells = <1>;
+				#size-cells = <0>;
 				timer@0 {
 					compatible = "atmel,tcb-timer";
 					reg = <0>;