target-i386: add lock mov cr0 = cr8

AMD CPUs featuring a shortcut to access CR8 even from 32-bit mode.
If you use the LOCK prefix with "mov CR0", it accesses CR8 instead.
This behavior is guarded by the CR8_LEGACY CPUID bit
(Fn8000_0001:ECX[1]).
Signed-off-by: NAndre Przywara <andre.przywara@amd.com>
Signed-off-by: NAurelien Jarno <aurelien@aurel32.net>

target-i386/translate.c

@@ -7351,6 +7351,10 @@ static target_ulong disas_insn(DisasContext *s, target_ulong pc_start)
                 ot = OT_QUAD;
             else
                 ot = OT_LONG;
+            if ((prefixes & PREFIX_LOCK) && (reg == 0) &&
+                (s->cpuid_ext3_features & CPUID_EXT3_CR8LEG)) {
+                reg = 8;
+            }
             switch(reg) {
             case 0:
             case 2: