vc4: Throttle outstanding rendering after submission.
vc4: Throttle outstanding rendering after submission.

Just make sure that after we've submitted, we get to at least 5
(global) submits ago before we go on to do more.  Prevents up to
seconds of lag with window movement in X with xcompmgr -c.  There may
be useful tuning to do in the future, but for now this gets us
usability.

Cc: "11.0 11.1" <59f39c0db42d4479a46b02d4d2bc11120e37bb44@lists.freedesktop.org>
Signed-off-by: Eric Anholt <96f164ad4d9b2b0dacf8ebee2bb1eeb3aa69adf1@anholt.net>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler