[RX51] Enable DRM in kernel
This enables DRM (Direct Rendering Manager) support in the kernel for the RX51. This opens up the possibility of using the Weston DRM backend, which in turn allows for DPMS (I hope) and other cool tricks.
n900:~# glxinfo|head name of display: :0 display: :0 screen: 0 direct rendering: Yes server glx vendor string: SGI server glx version string: 1.4
n900:~# glxgears 94 frames in 5.0 seconds = 18.772 FPS
Note, CONFIG_DRM_OMAP_CONNECTOR_ANALOG_TV
is required to work around the issue identified here: https://lkml.org/lkml/2017/6/30/191