i2c: designware: add SLAVE mode functions

- Changes in Kconfig to enable I2C_DESIGNWARE_SLAVE support
- Slave functions added to core library file
- Slave abort sources added to common source file
- New driver: i2c-designware-slave added
- Changes in the Makefile to compile the I2C_DESIGNWARE_SLAVE module
  when supported by the architecture.

All the SLAVE flow is added but it is not enabled via platform
driver.

Signed-off-by: Luis Oliveira <lolivei@synopsys.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
[wsa: made a function static and one-lined a message]
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>