gpio: put virtual gpio device into their own submenu

Since we already have a few virtual GPIO drivers, and more to come,
this category deserves its own submenu.
Signed-off-by: Enrico Weigelt, metux IT consult <info@metux.net>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>

drivers/gpio/Kconfig

@@ -1591,6 +1591,8 @@ config GPIO_VIPERBOARD
 
 endmenu
 
+menu "Virtual GPIO drivers"
+
 config GPIO_AGGREGATOR
 	tristate "GPIO Aggregator"
 	help
@@ -1614,4 +1616,6 @@ config GPIO_MOCKUP
 	  tools/testing/selftests/gpio/gpio-mockup.sh. Reference the usage in
 	  it.
 
+endmenu
+
 endif