meson: Fix evas engine install directory.

meson: Fix evas engine install directory.

Evas module loading code assumes engines are installed in
evas/modules/engines.

As part of the fixes building evas with meson, the engines are under a
subproject named evas/engines, causing the modules to be installed in
libdir/evas/engines/modules by default.

This commit adds a override of the directory the engine modules are
installed to use the correct location.

Reviewed-by: Marcel Hollerbach <mail@marcel-hollerbach.de>
Differential Revision: https://phab.enlightenment.org/D8693