ANDROID: GKI: pid: Export for find_task_by_vpid

    - Add EXPORT_SYMBOL_GPL for find_task_by_vpid() so that drivers
    can be loadable as a module.

    - This API is required by loadable driver module from samsung to
    read process related information based on pid and thread id.
    To get information on when a certain process or thread was started,
    duration of run, Average load contributed by it.

Signed-off-by: Abhilasha Rao <abhilasha.hv@samsung.corp-partner.google.com>
Bug: 158067689
Change-Id: I0db9cc50c93eedff0f3e9dea0ac09a5d17d118f0