mips: remove dma64_addr_t usage

dma64_addr_t looks pointless (at least there is no point that an
architecture has the own dma64_addr_t typedef).

dma_addr_t is set to 32 or 64 bits appropriately.  You can use u64 at
places where you know that 64 bit address is always necessary.

Let's use u64 instead for mips.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Cc: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>