Enhancement for avx-vnni patch

Enhancement for avx-vnni patch

1. Rename CpuVEX_PREFIX to PseudoVexPrefix and
   move it from cpu_flags to opcode_modifiers.
2. Delete {vex2} invalid test.
3. Use VexW0 and VexVVVV in the AVX-VNNI instructions.

gas/
	* config/tc-i386.c: Move Pseudo Prefix check to match_template.
	* testsuite/gas/i386/avx-vnni-inval.l: New file.
	* testsuite/gas/i386/avx-vnni-inval.s: Likewise.
	* testsuite/gas/i386/avx-vnni.d: Delete invalid {vex2} test.
	* testsuite/gas/i386/avx-vnni.s: Likewise.
	* testsuite/gas/i386/i386.exp: Add AVX VNNI invalid tests.
	* testsuite/gas/i386/x86-64-avx-vnni-inval.l: New file.
	* testsuite/gas/i386/x86-64-avx-vnni-inval.s: Likewise.
	* testsuite/gas/i386/x86-64-avx-vnni.d: Delete invalid {vex2} test.
	* testsuite/gas/i386/x86-64-avx-vnni.s: Likewise.

opcodes/
	* i386-opc.tbl: Rename CpuVEX_PREFIX to PseudoVexPrefix
	and move it from cpu_flags to opcode_modifiers.
	Use VexW0 and VexVVVV in the AVX-VNNI instructions.
	* i386-gen.c: Likewise.
	* i386-opc.h: Likewise.
	* i386-opc.h: Likewise.
	* i386-init.h: Regenerated.
	* i386-tbl.h: Likewise.