cgroup: increase maximum subsystem count from 16 to 32

cgroup: increase maximum subsystem count from 16 to 32

The current cgroup subsystem limit of 16 is insufficient, as the number of
existing subsystems has already reached this limit. When adding a new
subsystem that is not yet in the mainline kernel, building with
`make allmodconfig` requires first bypassing the
`BUILD_BUG_ON(CGROUP_SUBSYS_COUNT > 16)` restriction to allow compilation
to succeed. However, the kernel still fails to boot afterward.

This patch increases the maximum number of supported cgroup subsystems from
16 to 32, providing enough room for future subsystem additions.

Signed-off-by: Chen Ridong <chenridong@huawei.com>
Acked-by: Waiman Long <longman@redhat.com>
Tested-by: JP Kobryn <inwardvessel@gmail.com>
Acked-by: JP Kobryn <inwardvessel@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>