package/efl/libevas: add optional dependency on libfribidi

Fix the following message when libfribidi is enabled but not already
built:
Package fribidi was not found in the pkg-config search path.
Perhaps you should add the directory containing `fribidi.pc'
No package 'fribidi' found

Signed-off-by: Fabio Porcedda <fabio.porcedda@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>