package/kodi: enable gconv libraries on glibc configurations

When a glibc toolchain is used, Kodi really requires the gconv
libraries to be installed, otherwise no text is rendered in the GUI.

[Thomas: slightly improve commit message.]

Signed-off-by: Julien Boibessot <julien.boibessot@armadeus.com>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Tested-by: "Maxime Hadjinlian" <maxime.hadjinlian@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>