xorg: simplify dependencies on X.org

Many packages used to depend on BR2_PACKAGE_XORG||BR2_PACKAGE_XORG7,
but this is useless since BR2_PACKAGE_XORG is a non-existing
configuration option. So, these depencies gets simplified to
BR2_PACKAGE_XORG7 only.

Some others were depending on BR2_PACKAGE_TINYX (which doesn't) exist
or BR2_PACKAGE_XSERVER_xorg || BR2_PACKAGE_XSERVER_tiny ||
BR2_PACKAGE_XSERVER_x11r7. Replace all that mess by a simple
dependency on BR2_PACKAGE_XORG7.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>