PowerPC: Drop linkstation_HGLAN support

With changes to the rtl8169 ethernet to improve cache support, we have
needed additional cache functions for mpc8245.  As the board maintainer
has been unresponsive, remove this board.

Cc: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Tom Rini <trini@ti.com>