SGISEEQ: use cached memory access to make driver work on IP28

- Use inline functions for dma_sync_* instead of macros
- added Kconfig change to make selection for similair SGI boxes easier

Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Acked-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>