misc: MAX8997: Remove max8997-muic driver

This patch remove old max8997-muic drvier because of newly Extcon framework.
Extcon framework manages the external connector, so add extcon-max8997 driver
by using Extcon interface to support MUIC feature of Maxim 8997 PMIC instead
of max8997-muic driver(drivers/misc/max8997-muic.c).

Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: Myungjoo Ham <myungjoo.ham@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>