sx126x: refactor to RadioController interface to more easily handle non-STM32WL boards and remove duplicated code

Signed-off-by: deadprogram <ron@hybridgroup.com>

examples/sx126x/lora_continuous/radio_stm32wl.go

@@ -0,0 +1,15 @@
+//go:build stm32wlx
+
+package main
+
+import (
+	"machine"
+
+	"tinygo.org/x/drivers/sx126x"
+)
+
+var spi = machine.SPI3
+
+func newRadioControl() sx126x.RadioController {
+	return sx126x.NewRadioControl()
+}