winsys/amdgpu: Make KMS handles valid for original DRM file descriptor

winsys/amdgpu: Make KMS handles valid for original DRM file descriptor

Getting a DMA-buf fd and converting that to a handle using our duplicate
of that file descriptor (getting at which requires passing a
radeon_winsys pointer to the buffer_get_handle hook) makes sure of this,
since duplicated file descriptors reference the same file description
and therefore the same GEM handle namespace.

This is necessary because libdrm_amdgpu may use a different DRM file
descriptor with a separate handle namespace internally, e.g. because it
always reuses any existing amdgpu_device_handle for the same device.
amdgpu_bo_export returns a handle which is valid for that internal
file descriptor.

Bugzilla: https://bugs.freedesktop.org/110903
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Tested-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>