platform: msm: Support VBUS detection using extcon framework

The 8996 automotive using kernel v3.18 supports gpio based
VBUS detection using Power supply object framework. In kernel
v4.4 the VBUS detection is supported using extcon framework.
The 8996 automotive is being ported to kernel v4.4.
Hence add support for gpio based VBUS using extcon framework.

Change-Id: Ic63b5f84d57d18325cc6c8db24157d835284257f
Signed-off-by: Sriharsha Allenki <sallenki@codeaurora.org>