etnaviv: gallium driver for Vivante GPUs

This driver supports a wide range of Vivante IP cores like GC880,
GC1000, GC2000 and GC3000.

Changes from V1 -> V2:
 - added missing files to actually integrate the driver into build system.
 - adapted driver to new renderonly API

Signed-off-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Russell King <rmk@arm.linux.org.uk>
Signed-off-by: Wladimir J. van der Laan <laanwj@gmail.com>
Acked-by: Emil Velikov <emil.velikov@collabora.com>

src/gallium/auxiliary/pipe-loader/pipe_loader_drm.c

@@ -154,6 +154,11 @@ static const struct drm_driver_descriptor driver_descriptors[] = {
         .create_screen = pipe_vc4_create_screen,
         .configuration = configuration_query,
     },
+    {
+        .driver_name = "etnaviv",
+        .create_screen = pipe_etna_create_screen,
+        .configuration = configuration_query,
+    }
 };
 #endif