qca_7k: Replace BSD boilerplate with SPDX

According to MODULE_LICENSE the driver is under a dual license.
So replace the BSD license text with the proper SPDX tag.

Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Stefan Wahren <wahrenst@gmx.net>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>