Enable Intel RDPID instruction.

This patch enables Intel RDPID instruction described in Intel64 and
IA-32 Architectures Software Developer's Manual, April 2016.

gas/

	* config/tc-i386.c (cpu_arch): Add RDPID.
	* doc/c-i386.texi: Document RDPID.

gas/testsuite/

	* gas/i386/i386.exp: Run RDPID tests.
	* gas/i386/prefix.d: Adjust.
	* gas/i386/rdpid.s: New test.
	* gas/i386/rdpid.d: Ditto.
	* gas/i386/rdpid-intel.d: Ditto.
	* gas/i386/x86-64-rdpid.s: Ditto.
	* gas/i386/x86-64-rdpid.d: Ditto.
	* gas/i386/x86-64-rdpid-intel.d: Ditto.

opcodes/

	* i386-dis.c (prefix_table): Add RDPID instruction.
	* i386-gen.c (cpu_flag_init): Add RDPID flag.
	(cpu_flags): Add RDPID bitfield.
	* i386-opc.h (enum): Add RDPID element.
	(i386_cpu_flags): Add RDPID field.
	* i386-opc.tbl: Add RDPID instruction.
	* i386-init.h: Regenerate.
	* i386-tbl.h: Regenerate.