drivers: bbram: fix npcx driver and update Kconfig defaults

There was a typo that snuck into the bbram driver for npcx.
Fix the driver and update the Kconfig to automatically include the
driver if the compatible string exists in the dts. This ensures that
the driver is built when building the npcx evbs.

Signed-off-by: Yuval Peress <peress@chromium.org>