bcmframebuffer: Reject depths other than 16 on RPi 5

The Raspberry Pi 5 supports only depth 16 in the firmware.

Issue #511

lib/bcmframebuffer.cpp

@@ -2,7 +2,7 @@
 // bcmframebuffer.cpp
 //
 // Circle - A C++ bare metal environment for Raspberry Pi
-// Copyright (C) 2014-2020  R. Stange <[email protected]>
+// Copyright (C) 2014-2024  R. Stange <[email protected]>
 //
 // This program is free software: you can redistribute it and/or modify
 // it under the terms of the GNU General Public License as published by
@@ -141,6 +141,14 @@ void CBcmFrameBuffer::SetPalette32 (u8 nIndex, u32 nRGBA)
 
 boolean CBcmFrameBuffer::Initialize (void)
 {
+#if RASPPI >= 5
+	// The Raspberry Pi 5 supports only depth 16 in the firmware.
+	if (m_nDepth != 16)
+	{
+		return FALSE;
+	}
+#endif
+
 	if (m_nDisplay >= GetNumDisplays ())
 	{
 		return FALSE;