i2c: designware: Group all DesignWare drivers under a single option

There are quite a few drivers and options for the DesignWare
I2C adapter in the Kconfig. Grouping all of them under the
I2C_DESIGNWARE_CORE. That makes the menuconfig a bit more
easier to understand.

Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Acked-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>