target/mips: Convert Rel6 LDL/LDR/SDL/SDR opcodes to decodetree

LDL/LDR/SDL/SDR opcodes have been removed from the Release 6.

Add a single decodetree entry for the opcodes, triggering
Reserved Instruction if ever used.

Remove unreachable check_insn_opc_removed() calls.

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20201208203704.243704-12-f4bug@amsat.org>

target/mips/mips64r6.decode

@@ -12,6 +12,13 @@
 
 &rtype              rs rt rd sa !extern
 
+&REMOVED            !extern
+
 @lsa                ...... rs:5 rt:5 rd:5 ... sa:2 ......   &rtype
 
 DLSA                000000 ..... ..... ..... 000 .. 010101  @lsa
+
+REMOVED             011010 ----- ----- ----------------     # LDL
+REMOVED             011011 ----- ----- ----------------     # LDR
+REMOVED             101100 ----- ----- ----------------     # SDL
+REMOVED             101101 ----- ----- ----------------     # SDR

target/mips/translate.c

@@ -28870,11 +28870,10 @@ static bool decode_opc_legacy(CPUMIPSState *env, DisasContext *ctx)
         if (ctx->insn_flags & INSN_R5900) {
             check_insn_opc_user_only(ctx, INSN_R5900);
         }
+        check_insn_opc_removed(ctx, ISA_MIPS_R6);
         /* fall through */
     case OPC_LDL:
     case OPC_LDR:
-        check_insn_opc_removed(ctx, ISA_MIPS_R6);
-        /* fall through */
     case OPC_LWU:
     case OPC_LD:
         check_insn(ctx, ISA_MIPS3);
@@ -28883,8 +28882,6 @@ static bool decode_opc_legacy(CPUMIPSState *env, DisasContext *ctx)
         break;
     case OPC_SDL:
     case OPC_SDR:
-        check_insn_opc_removed(ctx, ISA_MIPS_R6);
-        /* fall through */
     case OPC_SD:
         check_insn(ctx, ISA_MIPS3);
         check_mips_64(ctx);