power: smb5-lib: Add sysfs entry to enable/disable moisture detection

Android userspace HAL expects an interface to dynamically
enable/disable moisture detection, add support for
same via the iio interface.

Change-Id: I8fb48807fb368ff78220623aaaee9f4877d1b918
Signed-off-by: Kavya Nunna <knunna@codeaurora.org>