Add IIO kernel config for Witherspoon

The CONFIG_IIO is depended by CONFIG_BMP280.

Change-Id: I543dac0485b6ebdc0c86397f61ac62e99e13fd6f
Signed-off-by: Lei YU <mine260309@gmail.com>
diff --git a/meta-witherspoon/recipes-kernel/linux/linux-obmc/witherspoon.cfg b/meta-witherspoon/recipes-kernel/linux/linux-obmc/witherspoon.cfg
index c5fe514..6d74746 100644
--- a/meta-witherspoon/recipes-kernel/linux/linux-obmc/witherspoon.cfg
+++ b/meta-witherspoon/recipes-kernel/linux/linux-obmc/witherspoon.cfg
@@ -3,4 +3,5 @@
 CONFIG_SENSORS_MAX31785=y
 CONFIG_SENSORS_UCD9000=y
 CONFIG_RTC_DRV_RV8803=y
+CONFIG_IIO=y
 CONFIG_BMP280=y