update-all-config.pl: only chdir into each project once

update-all-config.pl: only chdir into each project once

Since running the external find needs to first have a chdir
performed to the project directory it does not make sense to
do that for every external find command while not doing it
for the script itself.

This creates unnecessary chdir calls and makes the script
more complex than it needs to be.

Instead chdir to the project just once and simplify all
the project processing code to expect that to be the case.

Signed-off-by: Kyle J. McKay <mackyle@gmail.com>