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

extcon-gpio driver currently doesn't support passing the gpio extcon data
via device tree, we are adding this support so extcon-gpio driver can be
used with platforms using the DT from gpio extcon 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>
[cang@codeaurora.org: resolved conflicts due to removal of platform data]
Signed-off-by: Can Guo <cang@codeaurora.org>