bf609: enable soft switch gpio driver by default

Signed-off-by: Sonic Zhang <sonic.zhang@analog.com>

arch/blackfin/configs/BF609-EZKIT_defconfig

@@ -105,6 +105,7 @@ CONFIG_SPI=y
 CONFIG_SPI_ADI_V3=y
 CONFIG_GPIOLIB=y
 CONFIG_GPIO_SYSFS=y
+CONFIG_GPIO_MCP23S08=y
 # CONFIG_HWMON is not set
 CONFIG_WATCHDOG=y
 CONFIG_BFIN_WDT=y