boards/arm/*/*dts: fix double whitespace in model property

There is no reason to use double whitespaces in the dt
model property.

Signed-off-by: Antony Pavlov <[email protected]>

Author: frantony

boards/arm/hexiwear_k64/hexiwear_k64.dts

@@ -5,7 +5,7 @@
 #include <nxp/nxp_k6x.dtsi>
 
 / {
-	model = "Hexiwear K64  board";
+	model = "Hexiwear K64 board";
 	compatible = "nxp,hexiwear", "nxp,k64f", "nxp,k6x";
 
 	aliases {

boards/arm/stm32mp157c_dk2/stm32mp157c_dk2.dts

@@ -8,7 +8,7 @@
 #include <st/mp1/stm32mp157.dtsi>
 
 / {
-	model = "STMicroelectronics STM32MP157-DK2  board";
+	model = "STMicroelectronics STM32MP157-DK2 board";
 	compatible = "st,stm32mp157c-dk2", "st,stm32mp15";
 	chosen {
 		/*