fpga: lattice machxo2: Add Lattice MachXO2 support

This patch adds support to the FPGA manager for programming
MachXO2 device’s internal flash memory, via slave SPI.

Signed-off-by: Paolo Pisati <p.pisati@gmail.com>
[atull@kernel.org: use existing FPGA mgr API]
Signed-off-by: Alan Tull <atull@kernel.org>
Signed-off-by: Moritz Fischer <mdf@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>