cpuinfo/i386: Detect GFNI as an AVX extension

We won't use the SSE GFNI instructions, so delay
detection until we know AVX is present.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

host/include/i386/host/cpuinfo.h

@@ -27,6 +27,7 @@
 #define CPUINFO_ATOMIC_VMOVDQU  (1u << 17)
 #define CPUINFO_AES             (1u << 18)
 #define CPUINFO_PCLMUL          (1u << 19)
+#define CPUINFO_GFNI            (1u << 20)
 
 /* Initialized with a constructor. */
 extern unsigned cpuinfo;