perl: Fix substitution madness

perl: Fix substitution madness

We're going around in circles trying to fix the sed expressions and making one case
work and others not work. This patch fixes the base configuration file so we have
non-overlapping substitutions. I've tried to significantly clean up various problems
that were occurring once and for all.

This will hopefully resolve all the issues people have been seeing with incorrect perl
paths.

(From OE-Core rev: 31ff70794ecc431431476f81c8934fff25383613)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>