[x64] Add kX64EmitAVX512VBMI feature-flag and detection

Allows access to byte-element 2-register permutations(32-byte look up
tables) and for 64-bit multi-shifts.
Particularly adding this to accelerate the assembly of our `PERMUTE`
opcode.

src/xenia/cpu/backend/x64/x64_backend.cc

@@ -42,6 +42,7 @@ DEFINE_int32(x64_extension_mask, -1,
              "  512 = AVX512VL\n"
              " 1024 = AVX512BW\n"
              " 2048 = AVX512DQ\n"
+             " 4096 = AVX512VBMI\n"
              "   -1 = Detect and utilize all possible processor features\n",
              "x64");