pca9468_charger: ramp down current on disable

Ramp all the way down PCA iin current by 100mA every 250ms before
switching to MW during WLC charging and then set vout to 4*vba to
avoid disconnects.

Bug: 194346461
Signed-off-by: AleX Pelosi <apelosi@google.com>
Change-Id: I1c453a84bfd51c9ad09e863abd8987416c9c796d