[iOS] Blacklist iOS with regards to bgra support

A number of devices are indicating that there is a problem with using
bgra so instead of blacklisting all of them individually it is best to
blacklist them all on the iOS platform. This ensures
QQuickItem::grabToImage() will work then.

Task-number: QTBUG-45902
Change-Id: I900857cfa996924469aaaeeee8037dc84a4fd575
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>

src/gui/opengl/qopenglframebufferobject.cpp

@@ -1282,6 +1282,7 @@ static inline QImage qt_gl_read_framebuffer_rgba8(const QSize &size, bool includ
     const char *ver = reinterpret_cast<const char *>(funcs->glGetString(GL_VERSION));
 
     // Blacklist GPU chipsets that have problems with their BGRA support.
+#ifndef Q_OS_IOS
     const bool blackListed = (qstrcmp(renderer, "PowerVR Rogue G6200") == 0
                              && ::strstr(ver, "1.3") != 0) ||
                              (qstrcmp(renderer, "Mali-T760") == 0
@@ -1289,7 +1290,9 @@ static inline QImage qt_gl_read_framebuffer_rgba8(const QSize &size, bool includ
                              (qstrcmp(renderer, "Mali-T720") == 0
                              && ::strstr(ver, "3.1") != 0) ||
                              qstrcmp(renderer, "PowerVR SGX 554") == 0;
-
+#else
+    const bool blackListed = true;
+#endif
     const bool supports_bgra = has_bgra_ext && !blackListed;
 
     if (supports_bgra) {