arm: socfpga: Add DW master SPI clock to clock_manager.c

This function will be needed by the upcoming Designware master SPI
driver.

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>