gpu: host1x: Add locking to syncpt

Currently syncpoints are not locked by mutex and this causes races
if we are aggressively freeing and allocating syncpoints.

This patch adds missing mutex protection to syncpoint structures.

Signed-off-by: Arto Merilainen <amerilainen@nvidia.com>
Reviewed-by: Shridhar Rasal <srasal@nvidia.com>
Signed-off-by: Mikko Perttunen <mperttunen@nvidia.com>
[treding@nvidia.com: use better label names, don't reset local variable]
Signed-off-by: Thierry Reding <treding@nvidia.com>