fusee: support low-voltage SDMMC mode

fusee/fusee-primary/src/supplies.h

@@ -18,14 +18,19 @@ enum switch_power_constants {
     /* MicroSD card */
     SUPPLY_MICROSD_REGULATOR = 6,
     SUPPLY_MICROSD_VOLTAGE = 3300000,
+    SUPPLY_MICROSD_LOW_VOLTAGE = 1800000,
 
 };
 
+
 /**
  * Enables a given power supply.
  *
  * @param supply The power domain on the Switch that is to be enabled.
+ * @param use_low_voltage If the supply supports multiple voltages, use the lower one.
+ *      Some devices start in a high power mode, but an can be switched to a lower one.
+ *      Set this to false unless you know what you're doing.
  */
-void supply_enable(enum switch_power_supply supply);
+void supply_enable(enum switch_power_supply supply, bool use_low_voltage);
 
 #endif