Add Mic_Prepare() callback

Allows client to lazily prepare microphone for recording.

Author: rileytestut

src/Platform.h

@@ -93,6 +93,8 @@ void LAN_DeInit();
 int LAN_SendPacket(u8* data, int len);
 int LAN_RecvPacket(u8* data);
 
+void Mic_Prepare();
+
 }
 
 #endif // PLATFORM_H

src/SPI.cpp

@@ -561,6 +561,8 @@ void Write(u8 val, u32 hold)
 
         case 0x60:
             {
+                Platform::Mic_Prepare();
+                
                 if (MicBufferLen == 0)
                     ConvResult = 0x800;
                 else