sandbox, test: add test for GPIO_HOG function

currently gpio hog function is not tested with "ut dm gpio"
so add some basic tests for gpio hog functionality.

For this enable GPIO_HOG in sandbox_defconfig, add
in DTS some gpio hog entries, and add testcase in
"ut dm gpio" command.

Signed-off-by: Heiko Schocher <hs@denx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/sandbox/dts/test.dts b/arch/sandbox/dts/test.dts
index 5ce5e28..24bb3ce 100644
--- a/arch/sandbox/dts/test.dts
+++ b/arch/sandbox/dts/test.dts
@@ -343,6 +343,26 @@
 			#gpio-cells = <1>;
 			gpio-bank-name = "a";
 			sandbox,gpio-count = <20>;
+			hog_input_active_low {
+				gpio-hog;
+				input;
+				gpios = <0 GPIO_ACTIVE_LOW>;
+			};
+			hog_input_active_high {
+				gpio-hog;
+				input;
+				gpios = <1 GPIO_ACTIVE_HIGH>;
+			};
+			hog_output_low {
+				gpio-hog;
+				output-low;
+				gpios = <2 GPIO_ACTIVE_HIGH>;
+			};
+			hog_output_high {
+				gpio-hog;
+				output-high;
+				gpios = <3 GPIO_ACTIVE_HIGH>;
+			};
 		};
 
 		gpio_b: extra-gpios {