fpga: dfl: add support for N3000 Nios private feature

fpga: dfl: add support for N3000 Nios private feature

This patch adds support for the Nios handshake private feature on Intel
PAC (Programmable Acceleration Card) N3000.

The Nios is the embedded processor on the FPGA card. This private feature
provides a handshake interface to FPGA Nios firmware, which receives
retimer configuration command from host and executes via an internal SPI
master (spi-altera). When Nios finishes the configuration, host takes over
the ownership of the SPI master to control an Intel MAX10 BMC (Board
Management Controller) Chip on the SPI bus.

For Nios firmware handshake part, this driver requests the retimer
configuration for Nios firmware on probe, and adds some sysfs nodes for
user to query the onboard retimer's working mode and Nios firmware
version.

For SPI part, this driver adds a spi-altera platform device as well as
the MAX10 BMC spi slave info. A spi-altera driver will be matched to
handle the following SPI work.

[mdf@kernel.org: Fixed up ABI doc kernel release]

Reviewed-by: Tom Rix <trix@redhat.com>
Signed-off-by: Xu Yilun <yilun.xu@intel.com>
Signed-off-by: Wu Hao <hao.wu@intel.com>
Signed-off-by: Matthew Gerlach <matthew.gerlach@linux.intel.com>
Signed-off-by: Russ Weight <russell.h.weight@intel.com>
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Link: https://lore.kernel.org/r/20210107043714.991646-8-mdf@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>