i2c: designware: Get rid of legacy platform data

Platform data is a legacy interface to supply device properties
to the driver. In this case we don't have anymore in-kernel users
for it. Just remove it for good.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Wolfram Sang <wsa@kernel.org>
Acked-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>