waf-cross-answers: Add cross-answers-mipsel.txt

Build fails on "mipsel" platforms due to missing cross-answers-mipsel.txt.
Fix this by linking it to cross-answers-mips.txt, since there's no hint
of taking endianess into account.

Signed-off-by: Mike Looijmans <mike.looijmans@topic.nl>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Joe MacDonald <joe_macdonald@mentor.com>