radeonsi: fix a hang with streamout on Hawaii

I actually couldn't reproduce this one, but internal docs recommend this
workaround. Better safe than sorry.

Also, the number of dwords for the sync packets is increased by 4 instead
of 2, because it wasn't bumped last time when a new packet was added there.

Cc: mesa-stable@lists.freedesktop.org
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
2 files changed