misc: Add Lattice ECP3 FPGA configuration via SPI

This patch adds support for bitstream configuration (programming /
loading) of the Lattice ECP3 FPGA's via the SPI bus.

Here an example on my custom MPC5200 based board:

$ echo 1 > /sys/class/firmware/spi0.0/loading
$ cat fpga_a4m2k.bit > /sys/class/firmware/spi0.0/data
$ echo 0 > /sys/class/firmware/spi0.0/loading

leads to these messages:

lattice-ecp3 spi0.0: FPGA Lattice ECP3-35 detected
lattice-ecp3 spi0.0: Configuring the FPGA...
lattice-ecp3 spi0.0: FPGA succesfully configured!

Signed-off-by: Stefan Roese <sr@denx.de>
Acked-by: Ming Lei <ming.lei@canonical.com>
Reviewed-by: Grant Likely <grant.likely@secretlab.ca>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>