feat: implement privileged mode support

src/main/scala/csr/PrivilegeControl.scala

@@ -2,20 +2,14 @@ import chisel3._
 
 class PrivilegeControl(p: CoreParams = CoreParams()) extends Module {
   val io = IO(new Bundle {
-    val trap = Input(Bool())
-    val mret = Input(Bool())
-    val sret = Input(Bool())
-    val privilege = Output(UInt(2.W))
+    val nextPriv = Input(UInt(2.W))
+    val setPriv = Input(Bool())
+    val priv = Output(UInt(2.W))
   })
 
-  val mode = RegInit(3.U(2.W))
-  when(io.trap) {
-    mode := 3.U
-  }.elsewhen(io.mret) {
-    mode := 0.U
-  }.elsewhen(io.sret) {
-    mode := 0.U
+  val privReg = RegInit(Privileged.PRV_M)
+  when(io.setPriv) {
+    privReg := io.nextPriv
   }
-  io.privilege := mode
+  io.priv := privReg
 }
-