Add basic ADC support

Planning on abstracting this behind hardware setup APIs, but this works
for a simple demo until then

core/main.c

@@ -5,10 +5,12 @@
 
 #include "core/ble.h"
 #include "core/routine.h"
+#include "core/hardware/adc.h"
 
 
 int main(void)
 {
+    adc_init();
     routine_init();
     ble_init();