drm/amdkfd: Add multiple kgd support

The current code can only support one kgd instance. We have to
support multiple kgd instances in one system. i.e two amdgpu or two
radeon or one amdgpu + one radeon or more than two kgd instances.

Signed-off-by: Xihan Zhang <xihan.zhang@amd.com>
Signed-off-by: Oded Gabbay <oded.gabbay@amd.com>