watchdog: ftwdt010: return a previously deleted driver now ported to DM

The ftwdt010 watchdog driver was deleted by
commit 11232139 ("nds32: Remove the architecture")

Return it to the codebase in a DM compatible form. Enable it in
sandbox_defconfig to test compilability.
Another platform using ftwdt010 will be submitted later.

Signed-off-by: Sergei Antonov <saproj@gmail.com>
Reviewed-by: Stefan Roese <sr@denx.de>