These should be merged with existing files and the new files copied to the appropriate locations. Ensure that these driver files are in the kernel .config file.
kernel/hikey-linaro/drivers/usb/serial/sierra.c is the Sierra Wireless serial driver file. It should be copied to the appropriate location, overwriting any existing file. Ensure that this driver is ENABLED while the qcserial driver is DISABLED in the kernel .config file.