Add SWIOTLB config option and related files to Netlogic platform.

Some XLP SoC components like the SD/MMC interface cannot do DMA beyond
32-bit physical address. The SD/MMC driver can use memory outside this
range for IO, to support this we have to add bounce buffers implemented
by SWIOTLB.
Signed-off-by: Jayachandran C <jchandra@broadcom.com>
Cc: linux-mips@linux-mips.org
Cc: Ganesan Ramalingam <ganesanr@broadcom.com>
Patchwork: https://patchwork.linux-mips.org/patch/5410/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>