The DRM properties container must be destroyed with
drmModeFreeObjectProperties, and the connectors must be freed on every
caller. Also make it sure that gbm_device structs are destroyed with the
MetaRendererNativeGpuData that owns them.
https://bugzilla.gnome.org/show_bug.cgi?id=789984
When drmHandleEvent() returns an error and errno is set to EAGAIN,
instead of ending up in a busy loop, poll() the fd until there is
anything to read.
https://bugzilla.gnome.org/show_bug.cgi?id=785381
In order to eventually support multilpe GPUs with their own connectors,
split out related meta data management (i.e. outputs, CRTCs and CRTC
modes) into a new MetaGpu GObject.
The Xrandr backend always assumes there is always only a single "GPU" as
the GPU is abstracted by the X server; only the native backend (aside
from the test backend) will eventually see more than one GPU.
The Xrandr backend still moves some management to MetaGpuXrandr, in
order to behave more similarly to the KMS counterparts.
https://bugzilla.gnome.org/show_bug.cgi?id=785381
