extcon: storage-cd-gpio: add storage card detect gpio based extcon

This change adds the storage card detect GPIO based extcon driver to
support detecting removable UFS/SD cards hot plug events.

Change-Id: Ib0d927c7c75d8e2bb23eaebae17393efbd5cace9
Signed-off-by: Can Guo <cang@codeaurora.org>