platform/chrome: cros_usbpd_notify: Rename cros_ec_pd_command()

Rename cros_ec_pd_command()_to cros_ec_command() since it can be used
for sending any host command, and not just PD related ones.

This patch does not introduce any functional changes.

Signed-off-by: Prashant Malani <pmalani@chromium.org>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Link: https://lore.kernel.org/r/20210930022403.3358070-2-pmalani@chromium.org