MIPS: OCTEON: cvmx-bootinfo: add D-Link DSR-1000N

Add a definition for D-Link DSR-1000N router. The bootloader on this board
supplies 20006 in the bootinfo; the enum CVMX_BOARD_TYPE_CUST_DSR1000N
comes from the GPL sources of the board.

Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Cc: David Daney <ddaney.cavm@gmail.com>
Patchwork: https://patchwork.linux-mips.org/patch/7217/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>