add licenses

src/main/scala/xiangshan/backend/fu/fpu/FPToFP.scala

+// See LICENSE.Berkeley for license details.
+// See LICENSE.SiFive for license details.
+
 package xiangshan.backend.fu.fpu
 
 import chisel3._

src/main/scala/xiangshan/backend/fu/fpu/FPToInt.scala

+// See LICENSE.Berkeley for license details.
+// See LICENSE.SiFive for license details.
+
 package xiangshan.backend.fu.fpu
 
 import chisel3._

src/main/scala/xiangshan/backend/fu/fpu/IntToFP.scala

+// See LICENSE.Berkeley for license details.
+// See LICENSE.SiFive for license details.
+
 package xiangshan.backend.fu.fpu
 
 import chisel3._