drm/amdkfd: Process-device data creation and lookup split

This patch splits the current kfd_get_process_device_data() to two
functions, one that specifically creates a pdd and another one which
just do lookup.

This is done to enhance the readability and maintainability of the code.

Signed-off-by: Alexey Skidanov <Alexey.Skidanov@amd.com>
Signed-off-by: Oded Gabbay <oded.gabbay@amd.com>