target/i386: TCG supports 3DNow! prefetch(w)

The AMD prefetch(w) instructions have not been deprecated together with the rest
of 3DNow!, and in fact are even supported by newer Intel processor.  Mark them
as supported by TCG, as it supports all of 3DNow!.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

target/i386/cpu.c

@@ -647,7 +647,8 @@ void x86_cpu_vendor_words2str(char *dst, uint32_t vendor1,
           CPUID_EXT2_3DNOW | CPUID_EXT2_3DNOWEXT | CPUID_EXT2_PDPE1GB | \
           TCG_EXT2_X86_64_FEATURES)
 #define TCG_EXT3_FEATURES (CPUID_EXT3_LAHF_LM | CPUID_EXT3_SVM | \
-          CPUID_EXT3_CR8LEG | CPUID_EXT3_ABM | CPUID_EXT3_SSE4A)
+          CPUID_EXT3_CR8LEG | CPUID_EXT3_ABM | CPUID_EXT3_SSE4A | \
+          CPUID_EXT3_3DNOWPREFETCH)
 #define TCG_EXT4_FEATURES 0
 #define TCG_SVM_FEATURES (CPUID_SVM_NPT | CPUID_SVM_VGIF | \
           CPUID_SVM_SVME_ADDR_CHK)