sched: pre-allocate colocation groups

At present, sched_set_group_id() dynamically allocates structure for
colocation group to assign the given task to the group.  However
this can cause deadlock as memory allocator can wakeup a task which
also tries to acquire related_thread_group_lock.

Avoid such deadlock by pre-allocating colocation structures.  This
limits maximum colocation groups to static number but it's fine as it's
never expected to be a lot.

Change-Id: Ifc32ab4ead63c382ae390358ed86f7cc5b6eb2dc
Signed-off-by: Joonwoo Park <joonwoop@codeaurora.org>