arch: Create a base class for decoders.

This base class doesn't actually hold anything yet, it's just a place to
add shared functionality or interfaces later.

Change-Id: Ia33217bd78b1d1ff3df3b2202095576a4e5d8153
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/32897
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/arch/riscv/decoder.hh

@@ -31,6 +31,7 @@
 #define __ARCH_RISCV_DECODER_HH__
 
 #include "arch/generic/decode_cache.hh"
+#include "arch/generic/decoder.hh"
 #include "arch/riscv/isa_traits.hh"
 #include "arch/riscv/types.hh"
 #include "base/logging.hh"
@@ -42,7 +43,7 @@ namespace RiscvISA
 {
 
 class ISA;
-class Decoder
+class Decoder : public InstDecoder
 {
   private:
     DecodeCache::InstMap<ExtMachInst> instMap;