debugging: Simplify printing DrmObjects through QDebug

Summary:
Print automatically a few properties as well as the type, so it's easier
to read debug information.

Test Plan: Debugged a fix with it

Reviewers: #kwin, davidedmundson

Reviewed By: #kwin, davidedmundson

Subscribers: kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D28641

plugins/platforms/drm/drm_object.cpp

@@ -184,3 +184,8 @@ void DrmObject::Property::initEnumMap(drmModePropertyRes *prop)
 }
 
 }
+
+QDebug& operator<<(QDebug& s, const KWin::DrmObject* obj)
+{
+    return s.nospace() << "DrmObject(" << obj->id() << ", output:" << obj->output() << ", fd: "<< obj->fd() << ')';
+}

plugins/platforms/drm/drm_object.h

@@ -149,3 +149,4 @@ private:
 
 }
 
+QDebug& operator<<(QDebug& stream, const KWin::DrmObject*);