arm: socfpga: add functions to bring sdram, timer, and uart out of reset

These functions will be needed for use by the SPL for enabling the
console and sdram initialization.

Signed-off-by: Dinh Nguyen <dinguyen@opensource.altera.com>
Acked-by: Marek Vasut <marex@denx.de>
Acked-by: Pavel Machek <pavel@denx.de>