python: Set PIPE_TEXTURE_USAGE_RENDER_TARGET instead of DISPLAY_TARGET.

As the python state tracker is not integrated with window system an
cannot present surfaces directly.

src/gallium/state_trackers/python/samples/gs.py

@@ -136,7 +136,7 @@ def test(dev):
     cbuf = dev.texture_create(
         PIPE_FORMAT_X8R8G8B8_UNORM,
         width, height,
-        tex_usage=PIPE_TEXTURE_USAGE_DISPLAY_TARGET,
+        tex_usage=PIPE_TEXTURE_USAGE_RENDER_TARGET,
     ).get_surface()
     zbuf = dev.texture_create(
         PIPE_FORMAT_Z16_UNORM,

src/gallium/state_trackers/python/samples/tri.py

@@ -136,7 +136,7 @@ def test(dev):
     cbuf = dev.texture_create(
         PIPE_FORMAT_X8R8G8B8_UNORM, 
         width, height,
-        tex_usage=PIPE_TEXTURE_USAGE_DISPLAY_TARGET,
+        tex_usage=PIPE_TEXTURE_USAGE_RENDER_TARGET,
     ).get_surface()
     zbuf = dev.texture_create(
         PIPE_FORMAT_Z16_UNORM, 

src/gallium/state_trackers/python/tests/regress/fragment-shader/fragment-shader.py

@@ -114,7 +114,7 @@ def test(dev, name):
     cbuf = dev.texture_create(
         PIPE_FORMAT_X8R8G8B8_UNORM,
         width, height,
-        tex_usage=PIPE_TEXTURE_USAGE_DISPLAY_TARGET,
+        tex_usage=PIPE_TEXTURE_USAGE_RENDER_TARGET,
     ).get_surface()
     fb = Framebuffer()
     fb.width = width

src/gallium/state_trackers/python/tests/regress/vertex-shader/vertex-shader.py

@@ -114,7 +114,7 @@ def test(dev, name):
     cbuf = dev.texture_create(
         PIPE_FORMAT_X8R8G8B8_UNORM,
         width, height,
-        tex_usage=PIPE_TEXTURE_USAGE_DISPLAY_TARGET,
+        tex_usage=PIPE_TEXTURE_USAGE_RENDER_TARGET,
     ).get_surface()
     fb = Framebuffer()
     fb.width = width