Add explicit default constructor for QEglFSContext

Fixes Integrity compiler issue where it cannot find implicitly defined

Change-Id: I126333dd4b02b9b653b8e1ac5da07679b343c91f
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>
Reviewed-by: Kimmo Ollila <kimmo.ollila@qt.io>

src/plugins/platforms/eglfs/api/qeglfscontext_p.h

@@ -62,6 +62,7 @@ class Q_EGLFS_EXPORT QEglFSContext : public QEGLPlatformContext
 {
 public:
     using QEGLPlatformContext::QEGLPlatformContext;
+    QEglFSContext() = default; // workaround for INTEGRITY compiler
     QEglFSContext(const QSurfaceFormat &format, QPlatformOpenGLContext *share, EGLDisplay display,
                   EGLConfig *config);
     EGLSurface eglSurfaceForPlatformSurface(QPlatformSurface *surface) override;