usbc: Update tcpc_sop_prime_enable() description

Clearly mention that this function enables both SOP' and SOP'' messages.

Signed-off-by: Jianxiong Gu <jianxiong.gu@outlook.com>

include/zephyr/drivers/usb_c/usbc_tcpc.h

@@ -839,10 +839,11 @@ static inline int tcpc_set_low_power_mode(const struct device *dev, bool enable)
 }
 
 /**
- * @brief Enables the reception of SOP Prime messages
+ * @brief Enables the reception of SOP Prime and optionally SOP Double Prime messages
  *
  * @param dev     Runtime device structure
- * @param enable  Can receive SOP Prime messages when true, else it can not
+ * @param enable  Can receive SOP Prime messages and SOP Double Prime messages when true,
+ *		  else it can not
  *
  * @retval 0 on success
  * @retval -EIO on failure