x86/resctrl: Group struct rdt_hw_domain cleanup

domain_add_cpu() and domain_remove_cpu() need to kfree() the child
arrays that were allocated by domain_setup_ctrlval().

As this memory is moved around, and new arrays are created, adjusting
the error handling cleanup code becomes noisier.

To simplify this, move all the kfree() calls into a domain_free() helper.
This depends on struct rdt_hw_domain being kzalloc()d, allowing it to
unconditionally kfree() all the child arrays.

Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Jamie Iles <quic_jiles@quicinc.com>
Reviewed-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Tested-by: Xin Hao <xhao@linux.alibaba.com>
Tested-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
Tested-by: Cristian Marussi <cristian.marussi@arm.com>
Link: https://lore.kernel.org/r/20220902154829.30399-5-james.morse@arm.com