MIPS: bmips: include <linux/dma-direct.h> for phys_to_dma

Ensure this file has a prototype for phys_to_dma and dma_to_phys.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>