aspeed ast2400 enable aspeed-pwm-tacho

This enables the following for images built against the
meta-ast2400:
- aspeed-pwm-tacho

Change-Id: I89b3e56e98dd525104441946909c43b71ecd1366
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/meta-ast2400/recipes-kernel/linux/linux-obmc/defconfig b/meta-ast2400/recipes-kernel/linux/linux-obmc/defconfig
index b0cc79b..b9138d3 100644
--- a/meta-ast2400/recipes-kernel/linux/linux-obmc/defconfig
+++ b/meta-ast2400/recipes-kernel/linux/linux-obmc/defconfig
@@ -149,6 +149,7 @@
 CONFIG_SENSORS_LM25066=y
 CONFIG_SENSORS_UCD9000=y
 CONFIG_SENSORS_TMP421=y
+CONFIG_SENSORS_ASPEED=y
 # CONFIG_HID is not set
 # CONFIG_USB_SUPPORT is not set
 CONFIG_NEW_LEDS=y