sensors: add the sensors class support

Add a new sensors sysfs class and put all the sensors device driver
information in this class folder.

Change-Id: I7c35ec4642e4dbd264945ad3839914935b301af0
Signed-off-by: Jie Cheng <rockiec@codeaurora.org>
diff --git a/drivers/Kconfig b/drivers/Kconfig
index adead10..72440c9 100644
--- a/drivers/Kconfig
+++ b/drivers/Kconfig
@@ -152,4 +152,6 @@
 
 source "drivers/bif/Kconfig"
 
+source "drivers/sensors/Kconfig"
+
 endmenu