vgsp: client-session boundary fixes - WD ring scan gate + forced session flush

Two changes from the r839/r840 multi-client forensics (session 147):

1. The guest-RAM content scan for a GR ring must not run for the kernel
   RC-watchdog channel (h=0x31415900). Its ring is a plain kernel allocation
   always resolvable through the driver-published VAS walk; on r840 the walk
   lost a registration race, the scan latched a foreign garbage page, and
   the bad latch poisoned the driver's DMA test ('Failed to initialize DMA',
   Xorg died). Gated, the walk retries per pass; r841 Xorg#1 passes DMA
   (DMAFAIL=0) where r840 failed.

2. sema_force_flush module parameter + gsp_sema_service_sess_flush_force():
   execute the ISSUE-0002 client-session flush even with live channels. The
   channel-close trigger never fires on real boots (driver-global channels
   stay valid), so later client sessions inherited stale discovery state.
   Verified on r841: flush executes mid-boot, Xorg survives it and
   re-registers its channels.

Remaining wall (addendum 9): GR client channels' pushbuffer reads return
all-zero through the trusted translation (va=0x4000000-class, src=4), so
first entries never complete and GL clients never render.

0 files changed, 0 insertions, 0 deletions