power: supply: PCHG: Use MKBP for device event handling

This change makes the PCHG driver receive device events through
MKBP protocol since CrOS EC switched to deliver all peripheral
charge events to the MKBP protocol. This will unify PCHG event
handling on X86 and ARM.

Signed-off-by: Daisuke Nojiri <dnojiri@chromium.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>