winsys/amdgpu: Keep track of retrieved KMS handles using hash tables

winsys/amdgpu: Keep track of retrieved KMS handles using hash tables

The assumption being that KMS handles are only retrieved for relatively
few BOs, so hash tables should be efficient both in terms of performance
and memory consumption.

We use the address of struct amdgpu_winsys_bo as the key and its
kms_handle field (the KMS handle valid for the DRM file descriptor
passed to amdgpu_device_initialize) as the hash value.

v2:
* Add comment above amdgpu_screen_winsys::kms_handles (Pierre-Eric
  Pelloux-Prayer)
v3:
* Protect kms_handles hash table with amdgpu_winsys::sws_list_lock
  mutex.

Reviewed-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3202>