giflib: RDEPENDS on perl

The giflib utility "gifburst" is a Perl-script, so make sure Perl
is a run-time dependency for the giflib-utils package.

This will silence file-rdeps QA issue.

Signed-off-by: Magnus Olsson <magnus@minimum.se>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>