patman: Add a tools library for using temporary files

patman: Add a tools library for using temporary files

For tools which want to use input files and temporary output, it is useful
to have the handling of these dealt with in one place. Add a new library
which allows input files to be read, and output files to be written, all
based on a common directory structure.

Signed-off-by: Simon Glass <sjg@chromium.org>