[POWERPC] PS3: Remove lpar address workaround

Remove the PS3 workaround needed to support sparsemem SPU mappings.
The SPU mappings no longer use sparsemem, so this workaround is no
longer needed.

Signed-off-by: Geoff Levand <geoffrey.levand@am.sony.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>