drm/vmwgfx: Determine lock-waiting timeout from vblank state

drm/vmwgfx: Determine lock-waiting timeout from vblank state

Use the calculated duration of a frame as stored in the vblank state
for the lock-waiting timeout. Decouples the waiting from the details
of the vblank implementation. Both values should be equal.

This will be helpful for replacing vmwgfx's vblank timer with DRM's
common implementation.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Zack Rusin <zack.rusin@broadcom.com>
Link: https://patch.msgid.link/20260427150250.699768-2-tzimmermann@suse.de