Add Xiao RP2040 and RP2350 variants (#10109)

variants/rp2040/seeed_xiao_rp2040/variant.cpp

@@ -0,0 +1,10 @@
+#include <Arduino.h>
+
+// Turn off the green and blue LEDs, which are on by default.
+void initVariant()
+{
+    pinMode(PIN_LED_G, OUTPUT);
+    pinMode(PIN_LED_B, OUTPUT);
+    digitalWrite(PIN_LED_G, HIGH);
+    digitalWrite(PIN_LED_B, HIGH);
+}