ARM: socfpga: Add missing #reset-cells to socfpga device tree

add #reset-cells to socfpga.dtsi. This was missing from the
latest updates and caused the socfpga reset controller to fail
to load like so:

ffd05000.rstmgr: /soc/rstmgr@ffd05000 missing #reset-cells property
probe of ffd05000.rstmgr failed with error -22

Signed-off-by: Vince Bridgers <vbridgers2013@gmail.com>
Signed-off-by: Dinh Nguyen <dinguyen@altera.com>
Signed-off-by: Olof Johansson <olof@lixom.net>