DMA: fix AMBA PL08x compilation issue with 64bit DMA address type

When dma_addr_t is 64 bits long, compilation of the AMBA PL08x DMA
driver breaks due to a missing 64bit%8bit modulo operation.
Looking more closely the divisor in these operations can only be
1, 2 or 4, so the full featured '%' modulo operation is overkill and
can be replaced with simple bit masking.

Change from v1:
Replace open-coded function with existing IS_ALIGNED macro and use a
macro around that to avoid a line becoming too long.

Signed-off-by: Andre Przywara <andre.przywara@linaro.org>
Acked-by: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Rob Herring <rob.herring@calxeda.com>