extcon: gpio: add support to parse platform data from device tree

extcon-gpio driver currently doesn't support passing the platfroom data via
device tree, we are adding this support so extcon-gpio driver can be used
with platforms using the DT from platform data. We are also fixing the
issue where we were passing the supported_cable incorrect way to
extcon_dev_allocate() API.

Change-Id: I035c2f6c43d6c5140bc9a3088da7c1b3f2f108f1
Signed-off-by: Subhash Jadavani <subhashj@codeaurora.org>