MIPS: generic: Add support for MIPSfpga

Add support for the MIPSfpga platform to generic kernel.

Signed-off-by: Zubair Lutfullah Kakakhel <Zubair.Kakakhel@imgtec.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/15846/


[jhogan@kernel.org: Use separate board-xilfpga.its.S. Add 32r2 and
 little endian requires to board-xilfpga.config]
Signed-off-by: James Hogan <jhogan@kernel.org>