drivers: watchdog: Use common name configuration for all drivers

Each driver seemed to use their own Kconfig option to set the name for
their drivers.  This makes writing example/test code difficult as each
one of them will have to special case for each of the supported
platforms.

Use a consistent CONFIG_WDT_0_NAME option in all drivers.

Fixes #8094.

Signed-off-by: Leandro Pereira <leandro.pereira@intel.com>