drm: Add support of ARC PGU display controller

ARC PGU could be found on some development boards from Synopsys.
This is a simple byte streamer that reads data from a framebuffer
and sends data to the single encoder.

Signed-off-by: Carlos Palminha <palminha@synopsys.com>
Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Cc: David Airlie <airlied@linux.ie>
Cc: dri-devel@lists.freedesktop.org
Cc: linux-snps-arc@lists.infradead.org

drivers/gpu/drm/Kconfig

@@ -281,3 +281,5 @@ source "drivers/gpu/drm/imx/Kconfig"
 source "drivers/gpu/drm/vc4/Kconfig"
 
 source "drivers/gpu/drm/etnaviv/Kconfig"
+
+source "drivers/gpu/drm/arc/Kconfig"