extcon: Add extcon_dev_allocate/free() to control the memory of extcon device

This patch add APIs to control the extcon device on extcon provider driver.
The extcon_dev_allocate() allocates the memory of extcon device and initializes
supported cables. And then extcon_dev_free() decrement the reference of the
device of extcon device and free the memory of the extcon device. This APIs
must need to implement devm_extcon_dev_allocate()/free() APIs.

Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>
Reviewed-by: Felipe Balbi <balbi@ti.com>