implement new decoder

TODO: need
- release version of chisel 3.6.1, 5.1
- Zb/Zbk support
- riscv-opcode path configurable

src/main/scala/rocket/CustomInstructions.scala → src/main/scala/deprecate/rocket/CustomInstructions.scala

@@ -4,6 +4,7 @@
 package freechips.rocketchip.rocket
 
 import chisel3.util._
+import freechips.rocketchip.rocket._
 
 object CustomInstructions {
   def MNRET              = BitPat("b01110000001000000000000001110011")

src/main/scala/rocket/Decode.scala → src/main/scala/deprecate/rocket/Decode.scala

@@ -5,6 +5,7 @@ package freechips.rocketchip.rocket
 import chisel3._
 import chisel3.util.BitPat
 import chisel3.util.experimental.decode._
+import freechips.rocketchip.rocket._
 
 object DecodeLogic
 {

src/main/scala/rocket/IDecode.scala → src/main/scala/deprecate/rocket/IDecode.scala

@@ -7,6 +7,7 @@ import chisel3._
 import chisel3.util._
 import org.chipsalliance.cde.config.Parameters
 import freechips.rocketchip.util._
+import freechips.rocketchip.rocket._
 import Instructions._
 import CustomInstructions._
 

src/main/scala/rocket/Instructions.scala → src/main/scala/deprecate/rocket/Instructions.scala

@@ -4,6 +4,7 @@
 package freechips.rocketchip.rocket
 
 import chisel3.util._
+import freechips.rocketchip.rocket._
 
 /* make EXTENSIONS="rv_* rv64*" inst.chisel */