arm: socfpga: Add socfpga_spim_enable() to reset_manager.c

arm: socfpga: Add socfpga_spim_enable() to reset_manager.c

This function will be needed by the upcoming Designware master SPI
driver. As the SPI master controller is held in reset by the current
Preloader implementation. So we need to release the reset for the
driver to communicate with the controller.

This function is called from arch_early_init_r() if the SPI
driver is enabled.

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>