meson: egl: correctly manage loader/xmlconfig

Earlier commit introduced support for haiku yet did not properly
annotate the loader/xmlconfig dependencies.

Thus we ended up adding inc_loader for each !haiku platform - see
659910ed 9a96bf0e c731508b ec6cb01e.

One piece remained though - the wayland platform. Hence the following
would fail:

 meson -Dgallium-drivers=etnaviv -Ddri-drivers=''\
       -Dtools=etnaviv -Dplatforms=wayland -Dglx=disabled \
       build/

Cc: Alexander von Gluck IV <kallisti5@unixzen.com>
Reported-by: Boris Brezillon <boris.brezillon@collabora.com>
Fixes: 834d2215 ("meson: Add Haiku platform support v4")
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Tested-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Eric Engestrom <eric.engestrom@intel.com>
Reviewed-by: Dylan Baker <dylan@pnwbakers.com>
(cherry picked from commit f0a7b463)