gpu: host1x: Fix hang on Tegra186+

Tegra186+ hangs if host1x hardware is disabled at a kernel boot time
because we touch hardware before runtime PM is resumed. Move sync point
assignment initialization to the RPM-resume callback. Older SoCs were
unaffected because they skip that sync point initialization.

Tested-by: Jon Hunter <jonathanh@nvidia.com> # T186
Reported-by: Jon Hunter <jonathanh@nvidia.com> # T186
Fixes: 6b6776e2 ("gpu: host1x: Add initial runtime PM and OPP support")
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>