MIPS: xilfpga: Add mipsfpga platform code

The xilfpga platform will be DT only.

Add required platform code.
DT files have already been added separately.

Signed-off-by: Zubair Lutfullah Kakakhel <Zubair.Kakakhel@imgtec.com>
Cc: robh+dt@kernel.org
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Cc: devicetree@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/11364/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>