[U-Boot] linkstation_HGLAN and MPC824x support

Hello,

With a recent change to U-Boot (as part of merging http://patchwork.ozlabs.org/patch/293612/), we need cache support for MPC824x, for the linkstation_HGLAN board to continue building, as the network driver is now cache aware.

Alternatively, if there is no interest in maintaining the platform upstream anymore, we can remove it. Thanks!