ARM: socfpga: Enable soft reset

Enable a cold or warm reset to the HW from userspace.

Also fix a few sparse errors:

warning: symbol 'sys_manager_base_addr' was not declared. Should it be static?
warning: symbol 'rst_manager_base_addr' was not declared. Should it be static?

Signed-off-by: Dinh Nguyen <dinguyen@altera.com>
Reviewed-by: Pavel Machek <pavel@denx.de>
Signed-off-by: Olof Johansson <olof@lixom.net>