extcon: Redefine the unique id of supported external connectors without 'enum extcon' type

This patch just redefine the unique id of supported external connectors without
'enum extcon' type. Because unique id would be used on devictree file(*.dts) to
indicate the specific external connectors like key number of input framework.
So, I have the plan to move this definitions to following header file which
includes the unique id of supported external connectors.
- include/dt-bindings/extcon/extcon.h

Fixes: 2a9de9c0 ("extcon: Use the unique id for external connector instead of string")
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>