spi: Add Designware SPI controller Kconfig entry

spi: Add Designware SPI controller Kconfig entry

Add DWC SPI controller Kconfig entry.

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