vgsp: author the scrub release pair for scanner-registered waits (CONT.414)

The X DDX vidheap scrub wait polls the finish payload at channel buffer
+0x6c004 while the host still reads USERD GP_PUT=0, so put-based forward
authoring wrote sema=entries-1 / fin=0: exactly the values that leave
channelWaitForFreeEntry and channelWaitForFinishPayload blocked. Xorg then
held the NVRM RM API write lock inside NV_ESC_RM_VID_HEAP_CONTROL, and the
GL thread and nvidia-modeset both sat D-state on os_acquire_rwlock_write.

A scanner-registered buffer with no observed submissions now gets the
proven all-ones release pair (sema=fin=0xffffffff) and is re-authored every
pass so a guest rewrite cannot re-block the wait. Put-driven records keep
forward-only authoring.

Result: the GL thread leaves D-state and a glClear+glFinish+glReadPixels
probe returns rc=0 with pixel=ff0000ff (a real red readback).

0 files changed, 0 insertions, 0 deletions