package/libevas-generic-loaders: add libraw dependency

libraw it's one of the "highly recommended" dependecies
according to the README [1].

[1] https://git.enlightenment.org/core/evas_generic_loaders.git/tree/README?id=v1.15.0#n31



Signed-off-by: Romain Naour <romain.naour@openwide.fr>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>