ARM: dts: socfpga: Rename socfpga_cyclone5_de0_{sockit,nano_soc}

Rename DT source for DE0 Nano SoC . The board name is really DE0-Nano-SoC
or Atlas SoC, and it is not to be confused with SoCkit board, which is a
different one. Rename the DT source file to match the board name and to
avoid this possible mixup with another different board.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Dinh Nguyen <dinguyen@kernel.org>
Cc: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>