drm/amdgpu: partial revert "remove ctx->lock" v2

This reverts commit 461fa7b0

.

We are missing some inter dependencies here so re-introduce the lock
until we have figured out what's missing. Just drop/retake it while
adding dependencies.

v2: still drop the lock while adding dependencies

Signed-off-by: Christian König <christian.koenig@amd.com>
Tested-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com> (v1)
Fixes: 461fa7b0

 ("drm/amdgpu: remove ctx->lock")
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220419110633.166236-1-christian.koenig@amd.com