build: Allow boards to disable digital input/output support

Allow the micro-controller code to be built without support for
regular gpio pins.  In this case, the code for endstops, steppers, and
gpiocmds will be disabled.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

src/simulator/Kconfig

@@ -7,4 +7,12 @@ config BOARD_DIRECTORY
     string
     default "simulator"
 
+config SIMULATOR_SELECT
+    bool
+    default y
+    select HAVE_GPIO
+    select HAVE_GPIO_ADC
+    select HAVE_GPIO_SPI
+    select HAVE_GPIO_HARD_PWM
+
 endif