power: supply: cpcap-charger: Simplify things with enable and disable

Let's turn cpcap_charger_set_state() into separate cpcap_charger_enable()
and cpcap_charger_disable() to simplify things, and to allow managing
status separately. This can be then used for the follow-up patches to
make battery full status behave a bit nicer.

Cc: Arthur Demchenkov <spinal.by@gmail.com>
Cc: Carl Philipp Klemm <philipp@uvos.xyz>
Cc: Merlijn Wajer <merlijn@wizzup.org>
Cc: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>