drm/vmwgfx: Drop svga_lock

This isn't actually protecting anything becuase:
- when running, ttm_resource_manager->use_type is protected through
  vmw_private->reservation_semaphore against concurrent execbuf or
  well anything else that might evict or reserve buffers
- during suspend/resume there's nothing else running, hence
  vmw_pm_freeze and vmw_pm_restore do not need to take the same lock.
- this also holds for the SVGA_REG_ENABLE register write

Hence it is safe to just remove that spinlock.

Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Reviewed-by: Zack Rusin <zackr@vmware.com>
Reviewed-by: Roland Scheidegger <sroland@vmware.com>
Cc: VMware Graphics <linux-graphics-maintainer@vmware.com>
Cc: Roland Scheidegger <sroland@vmware.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201211162942.3399050-1-daniel.vetter@ffwll.ch