matchbox-lib: fix dependencies

matchbox-lib build-depends on xlib_libXext, but forgets to select it.
It also build-depends on expat without selecting it, but it does need
it.

Fix that: select xlib_libXext, remove expat.

Add myself to developpers for matchbox packages.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Arnout Vandecappelle <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>