drm/vmwgfx: Stabilize the command buffer submission code

This commit addresses some stability problems with the command buffer
submission code recently introduced:

1) Make the vmw_cmdbuf_man_process() function handle reruns internally to
avoid losing interrupts if the caller forgets to rerun on -EAGAIN.
2) Handle default command buffer allocations using inline command buffers.
This avoids rare allocation deadlocks.
3) In case of command buffer errors we might lose fence submissions.
Therefore send a new fence after each command buffer error. This will help
avoid lengthy fence waits.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Sinclair Yeh <syeh@vmware.com>