radv: make sure to not submit any IBs when RADV_FORCE_FAMILY is set

To prevent GPU hangs.

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3654>

docs/envvars.html

@@ -583,6 +583,8 @@ Mesa EGL supports different sets of environment variables.  See the
    <dd>disable memory shaders cache</dd>
    <dt><code>nongg</code></dt>
    <dd>disable NGG for GFX10+</dd>
+   <dt><code>noop</code></dt>
+   <dd>do not submit any IBs</dd>
    <dt><code>nooutoforder</code></dt>
    <dd>disable out-of-order rasterization</dd>
    <dt><code>noshaderballot</code></dt>