package/efl: fix build with wepb

webpdemux support in webp is mandatory since version 1.25.0 and
https://github.com/Enlightenment/efl/commit/df06418b6f39f3b8d73631bda33308b67736bb9d

Fixes:
 - http://autobuild.buildroot.org/results/736357e669c35bd56e818c0c7fabd1b455f40a5f



Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Reviewed-by: Romain Naour <romain.naour@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>