softpipe: Enable PIPE_CAP_TGSI_TEXCOORD.

The tgsi_exec path can handle it, and otherwise when we start using NIR
our MAX_VARYINGS value will cause us to have VARYING_SLOT_VARx above the
maximum.

Reviewed-by: Dave Airlie <airlied@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6018>
diff --git a/src/gallium/drivers/softpipe/sp_screen.c b/src/gallium/drivers/softpipe/sp_screen.c
index 7066e2f..9e974ae 100644
--- a/src/gallium/drivers/softpipe/sp_screen.c
+++ b/src/gallium/drivers/softpipe/sp_screen.c
@@ -253,6 +253,7 @@
    case PIPE_CAP_CULL_DISTANCE:
    case PIPE_CAP_COPY_BETWEEN_COMPRESSED_AND_PLAIN_FORMATS:
    case PIPE_CAP_TGSI_ARRAY_COMPONENTS:
+   case PIPE_CAP_TGSI_TEXCOORD:
       return 1;
    case PIPE_CAP_CLEAR_TEXTURE:
       return 1;