platform/chrome: Add CrOS USB PD logging driver

The CrOS USB PD logging feature is logically separate functionality of
the charge manager, hence has its own driver. The driver logs the event
data for the USB PD charger available in some ChromeOS Embedded
Controllers.

Signed-off-by: Guenter Roeck <groeck@chromium.org>
[remove macro to APPEND_STRING and minor cleanups]
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>