habanalabs: save pid per userptr

Currently userptr endpoint in debugfs prints out virtual addresses
in the user process memory space, without specifying their owner process
ID. User space virtual address is meaningless without knowing the owner
process.

Signed-off-by: Yuri Nudelman <ynudelman@habana.ai>
Reviewed-by: Oded Gabbay <ogabbay@kernel.org>
Signed-off-by: Oded Gabbay <ogabbay@kernel.org>