spi: Add designware master SPI DM driver used on SoCFPGA

This patch adds the driver for the Designware master SPI controller. This
IP core is integrated on the Altera SoCFPGA. This implementation is a
driver model (DM) implementation. So multiple SPI drivers can be used.
Thats necessary, since SoCFPGA also integrates the Cadence QSPI controller
used to connect the SPI NOR flashes. Without DM, using multiple SPI
drivers is not possible.

This driver is very loosely based on the Linux driver. Most of the Linux
driver is removed. Only the polling loop for the transfer is really used
from this driver, as we don't support interrupts and DMA right now.

This is tested on the SoCrates SoCFPGA board using the SPI pins on the
P14 header.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Chin Liang See <clsee@altera.com>
Cc: Dinh Nguyen <dinguyen@altera.com>
Cc: Vince Bridgers <vbridger@altera.com>
Cc: Marek Vasut <marex@denx.de>
Cc: Pavel Machek <pavel@denx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
Cc: Jagannadha Sutradharudu Teki <jagannadh.teki@gmail.com>