ion: add new ion_user_handle_t type for the user-space token

Declare new ion_user_handle_t type to contain the token returned to user-space.
This allows a 2-step migration of the user-space code to a new kernel header
first, then will allow us to change the definition of the ion_user_handle_type_t
to int without breaking the API.

Change-Id: I4200b6600df8e56fe98cf1580a13a65cb25ec646
Signed-off-by: Rom Lemarchand <romlem@google.com>
sync: Fix a race condition between release_obj and print_obj

Before this change, a timeline would only be removed from the timeline
list *after* the sync driver had its release_obj() called. However, the
driver's release_obj() may free resources needed by print_obj().

Although the timeline list is locked when print_obj() is called, it is
not locked when release_obj() is called. If one CPU was in print_obj()
when another was in release_obj(), the print_obj() may make unsafe
accesses.

It is not actually necessary to hold the timeline list lock when calling
release_obj() if the call is made after the timeline is unlinked from
the list, since there is no possibility another thread could be in --
or enter -- print_obj() for that timeline.

This change moves the release_obj() call to after the timeline is
unlinked, preventing the above race from occurring.

Signed-off-by: Alistair Strachan <alistair.strachan@imgtec.com>