ANDROID: input: elan_i2c: add elan touchpad driver

ANDROID: input: elan_i2c: add elan touchpad driver

SMbus and I2C handling from driver core into separate
transport modules and makes them optional.

This driver pick up from chromium 3.14-kernel
Here is the URL:
https://chromium.googlesource.com/chromiumos/third_party/kernel/+/v3.14

----Note a bit different-----
we can easy replace the reinit_completion(completion);
with "completion->done = 0" in driver.

Change-Id: Idf373a502faea7913889f4a2f14ba71cae0da5b8
Signed-off-by: Caesar Wang <wxt@rock-chips.com>