extcon: Add resource-managed extcon register function

Add resource-managed extcon device register function for convenience.
For example, if a extcon device is attached with new
devm_extcon_dev_register(), that extcon device is automatically
unregistered on driver detach.

Signed-off-by: Sangjung Woo <sangjung.woo@samsung.com>
[Fix bug about devm_extcon_dev_match/release() and code clean by Chanwoo Choi]
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>