i2c: designware: Let slave adapter support be optional

Only certain system configurations may use the I2C slave mode so let the
support be optional. This allow reducing module size if needed:

   text    data     bss     dec     hex filename
  10328    1336      16   11680    2da0 drivers/i2c/busses/i2c-designware-core.ko
   7222    1136       8    8366    20ae drivers/i2c/busses/i2c-designware-core.ko
Signed-off-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Tested-by: Luis Oliveira <lolivei@synopsys.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

drivers/i2c/busses/Kconfig

@@ -483,7 +483,6 @@ config I2C_DESIGNWARE_CORE
 config I2C_DESIGNWARE_PLATFORM
 	tristate "Synopsys DesignWare Platform"
 	select I2C_DESIGNWARE_CORE
-	select I2C_DESIGNWARE_SLAVE
 	depends on (ACPI && COMMON_CLK) || !ACPI
 	help
 	  If you say yes to this option, support will be included for the

drivers/i2c/busses/i2c-designware-core.h

@@ -309,7 +309,11 @@ void i2c_dw_disable_int(struct dw_i2c_dev *dev);
 
 extern u32 i2c_dw_read_comp_param(struct dw_i2c_dev *dev);
 extern int i2c_dw_probe(struct dw_i2c_dev *dev);
+#if IS_ENABLED(CONFIG_I2C_DESIGNWARE_SLAVE)
 extern int i2c_dw_probe_slave(struct dw_i2c_dev *dev);
+#else
+static inline int i2c_dw_probe_slave(struct dw_i2c_dev *dev) { return -EINVAL; }
+#endif
 
 #if IS_ENABLED(CONFIG_I2C_DESIGNWARE_BAYTRAIL)
 extern int i2c_dw_probe_lock_support(struct dw_i2c_dev *dev);