ANDROID: force struct cgroup_taskset to be defined in KMI

struct cgroup_taskset is defined in kernel/cgroup/cgroup-internal.h,
however libabigail is not finding its definition based on the
instantiation of the hooks, so force it to be defined by defining a
dummy exported symbol. Since cgroup_taskset is defined in a
subsystem-private header, create a new vendor_hooks.c file in
kernel/cgroup to define the dummy symbol.

Update the XML with the new type definitions

Bug: 233047575
Signed-off-by: Todd Kjos <tkjos@google.com>
Change-Id: I7a2bf2a722bf5aec0c702f215d572cc8e5336f9a