mfd: cros_ec_dev: Only register PCHG device if present

Don't create a device for the peripheral charger (PCHG) if there aren't
any peripheral charger ports. This removes a device on most ChromeOS
systems, because the peripheral charger functionality isn't always
present.

Cc: Prashant Malani <pmalani@chromium.org>
Cc: Tzung-Bi Shih <tzungbi@kernel.org>
Cc: Daisuke Nojiri <dnojiri@chromium.org>
Cc: Benson Leung <bleung@chromium.org>
Cc: Guenter Roeck <groeck@chromium.org>
Cc: <chrome-platform@lists.linux.dev>
Signed-off-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Prashant Malani <pmalani@chromium.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20220419000408.3202635-1-swboyd@chromium.org