chromeec: Add function to retrieve usb c charger info

Add google_chromeec_get_usb_pd_power_info(), which will
call the EC_CMD_USB_PD_POWER_INFO host command to retrieve
the current and voltage info of the usb c charger.
Returns power info in watts.

BUG=b:37473486
BRANCH=None
TEST=output debug info to make sure that correct power
     is returned.

Change-Id: Ie14a0a6163e1c2699cb20b4422c8062164d92076
Signed-off-by: Shelley Chen <shchen@chromium.org>
Reviewed-on: https://review.coreboot.org/21771
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/ec/google/chromeec/ec.h

@@ -81,6 +81,15 @@ enum usb_charge_mode {
 };
 int google_chromeec_set_usb_charge_mode(u8 port_id, enum usb_charge_mode mode);
 int google_chromeec_set_usb_pd_role(u8 port, enum usb_pd_control_role role);
+/*
+ * Retrieve the charger type and max wattage.
+ *
+ * @param type      charger type
+ * @param max_watts charger max wattage
+ * @return non-zero for error, otherwise 0.
+ */
+int google_chromeec_get_usb_pd_power_info(enum usb_chg_type *type,
+					  u32 *max_watts);
 
 /* internal structure to send a command to the EC and wait for response. */
 struct chromeec_command {