Fix silabs compile - #elif without a condition replaced with #else (

#29319)

* Replace elif with else in macro

* Fix undefined usage of WriteQRCode as well

* Restyle

* Slightly better organization - a single ifdef in the header

* Refuse to compile the QRCodeScreen constant if qr code is not enabled

examples/platform/silabs/display/lcd.cpp

@@ -212,9 +212,11 @@ void SilabsLCD::SetScreen(Screen_e screen)
     case StatusScreen:
         WriteStatus();
         break;
+#ifdef QR_CODE_ENABLED
     case QRCodeScreen:
         WriteQRCode();
         break;
+#endif
     default:
         break;
     }
@@ -224,7 +226,7 @@ void SilabsLCD::CycleScreens(void)
 {
 #ifdef QR_CODE_ENABLED
     if (mCurrentScreen < QRCodeScreen)
-#elif
+#else
     if (mCurrentScreen < StatusScreen)
 #endif
     {

examples/platform/silabs/display/lcd.h

@@ -37,7 +37,9 @@ class SilabsLCD
     {
         DemoScreen = 0,
         StatusScreen,
+#ifdef QR_CODE_ENABLED
         QRCodeScreen,
+#endif
         InvalidScreen,
     } Screen_e;
 
@@ -74,13 +76,15 @@ class SilabsLCD
         bool protocol1 = false; /* data */
     } DemoState_t;
 
-    void WriteQRCode();
     void WriteDemoUI();
     void WriteStatus();
+
 #ifdef QR_CODE_ENABLED
+    void WriteQRCode();
     void LCDFillRect(uint8_t x, uint8_t y, uint8_t w, uint8_t h);
     char mQRCodeBuffer[chip::QRCodeBasicSetupPayloadGenerator::kMaxQRCodeBase38RepresentationLength + 1];
 #endif
+
     GLIB_Context_t glibContext;
 
 #ifdef SL_DEMO_NAME