extcon: Rename the extcon_set/get_state() to maintain the function naming pattern

This patch just renames the existing extcon_get/set_cable_state_()
as following because of maintaining the function naming pattern
like as extcon APIs for property.
- extcon_set_cable_state_() -> extcon_set_state()
- extcon_get_cable_state_() -> extcon_get_state()

But, this patch remains the old extcon_set/get_cable_state_() functions
to prevent the build break. After altering new APIs, remove the old APIs.

Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>
Tested-by: Chris Zhong <zyw@rock-chips.com>
Tested-by: Guenter Roeck <groeck@chromium.org>
Reviewed-by: Guenter Roeck <groeck@chromium.org>