mfd: cros: add charger port count command definition

A new more command has been added to the ChromeOS embedded controller
that allows to get the number of charger port count. Unlike
EC_CMD_USB_PD_PORTS, this new command also includes the dedicated
port if present.

This command will be used to expose the dedicated charger port
in the ChromeOS charger driver.

Signed-off-by: Fabien Parent <fparent@baylibre.com>
Acked-for-MFD-by: Lee Jones <lee.jones@linaro.org>
Reviewed-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>