percpu: move pcpu_lpage_build_unit_map() and pcpul_lpage_dump_cfg() upward

Unit map handling will be generalized and extended and used for
embedding sparse first chunk and other purposes.  Relocate two
unit_map related functions upward in preparation.  This patch just
moves the code without any actual change.

Signed-off-by: Tejun Heo <tj@kernel.org>