This refactoring task is to make page_zip_decompress_low() linkable with
external tools.

This RB is mainly about moving code around.
1. When functions are moved, it doesn't convert functions to doxygen
style.
2. it also doesn't fix existing issues according to coding guide lines

Reviewed-by: Kevin Lewis <kevin.lewis@oracle.com>
Reviewed-by: Debarun Banerjee <debarun.banerjee@oracle.com>
RB: 8611