drm/amdgpu: Replace VKMS vblank timer with common implementation

drm/amdgpu: Replace VKMS vblank timer with common implementation

Replace amdgpu's custom vblank timers with the shared implementation
in DRM's vblank code. Both are built upon hrtimers. The vblank logic
is identical.

The shared helpers contain all initialization internally. They also
handle a number of deadlocks and race conditions that are present in
amdgpu.

Also remove the set-but-unused field vsync_timer_enabled from struct
amdgpu_crtc.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>