spi: altera: Add DFL bus driver for Altera API Controller

This patch adds a Device Feature List (DFL) bus driver for the
Altera SPI Master controller.  The SPI master is connected to an
Intel SPI Slave to Avalon Bridge inside an Intel MAX10
BMC Chip.

Signed-off-by: Matthew Gerlach <matthew.gerlach@linux.intel.com>
Link: https://lore.kernel.org/r/20210416165720.554144-3-matthew.gerlach@linux.intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>