soc/intel_adsp: Fix the PFN width in cavs-fw.py loader

Change the PFN field width from 54 to 55 to follow the Linux Doc.
(https://www.kernel.org/doc/html/latest/admin-guide/mm/pagemap.html

)
Otherwise issue may arise if physical address beyond 2^66 is mapped.

Refactor the v15 and v25 scripts to extract the common part.
This is to suppress the pylint duplicate code check.

Signed-off-by: Shao Ming <ming.shao@intel.com>