gpu: ion: Fix debugfs handling of multiple kernel clients

Currently, Ion registers all debugfs entries for clients
via pid. If there are multiple kernel clients, this means
the debugfs entry only gets created for the first one. Fix
this by creating debugfs entries by name always. When
creating user clients, specify the name via the pid.

Change-Id: I00cbb284d1c53b3362bb7be9c0275620a9fac167
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>
Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>