X86: Fix address size handling so real mode works properly.

Virtual (pre-segmentation) addresses are truncated based on address size, and
any non-64 bit linear address is truncated to 32 bits. This means that real
mode addresses aren't truncated down to 16 bits after their segment bases are
added in.

src/arch/x86/isa/microops/ldstop.isa

@@ -361,7 +361,7 @@ let {{
     exec_output = ""
 
     calculateEA = '''
-    EA = bits(SegBase + scale * Index + Base + disp, addressSize * 8 - 1, 0);
+    EA = SegBase + bits(scale * Index + Base + disp, addressSize * 8 - 1, 0);
     '''
 
     def defineMicroLoadOp(mnemonic, code, bigCode='',

src/arch/x86/tlb.cc

@@ -281,6 +281,9 @@ TLB::translate(RequestPtr req, ThreadContext *tc, Translation *translation,
                     return new GeneralProtection(0);
             }
         }
+        if (m5Reg.mode != LongMode ||
+                (flags & (AddrSizeFlagBit << FlagShift)))
+            vaddr &= mask(32);
         // If paging is enabled, do the translation.
         if (m5Reg.paging) {
             DPRINTF(TLB, "Paging enabled.\n");