init.rc: migrate tasks from root cpu cgroup to a subgroup

Migrate tasks from root group to a subgroup would help us to put soft
cpu bandwidth control correctly. There are few tasks now failed to
migrate due to PF_NO_SETAFFINITY which is the default kernel behavior
which we are not overriding at this moment.

This CL also fixed an issue that most of RT thread lost RT attribute
when kernel with CONFIG_RT_GROUP_SCHED enabled, as the subgroup would be
initialized with 0 RT runtime by default. CONFIG_RT_GROUP_SCHED is not
enabled in GKI kernels but there could be devices with
CONFIG_RT_GROUP_SCHED enabled, so setting some budget for those devices
to make they can still function. OEM can either set proper budget by
themselves or remove CONFIG_RT_GROUP_SCHED completely.

Bug: 171740453
Test: boot and check cgroup
Change-Id: I83babad2751c61d844d03383cb0af09e7513b8e9