One issue exposed after below commit with which the system will freeze
at suspend after vGPU is created (no need to activate the vGPU).
commit e6ba7648 ("drm/i915: Remove i915->kernel_context")

Old implementation pin the intel_context at setup_submission and
unpin it at clean_submission. So after some vGPU is created, the
intel_context is always pinned there although no workload using it.
It will then block i915 enter suspend state.

There is no need to pin it all the time. Pin/unpin it around workload
lifecycle is more reasonable. After GVT enabled suspend/resume, the
pinned intel_context will also get unpined when userspace put VM process
into suspend state since all workloads are retired, then it's safe to
unpin all intel_context for workloads created. So move the pin/unpin to
create_workload and destroy_workload, while still keep the
create/destroy in old place.

V2:
Rebase.

Fixes: e6ba7648 ("drm/i915: Remove i915->kernel_context")
Reviewed-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Colin Xu <colin.xu@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20201016054059.238371-1-colin.xu@intel.com