Add support for Intel ENQCMD[S] instructions

Add support for Intel ENQCMD[S] instructions

This patch enables support for ENQCMD[S] in binutils.  Please refer to

https://software.intel.com/sites/default/files/managed/c5/15/architecture-instruction-set-extensions-programming-reference.pdf

for ENQCMD[S] details.

Make check-gas is ok.

gas/ChangeLog:

2019-06-04  Xuepeng Guo  <xuepeng.guo@intel.com>
	    Lili Cui  <lili.cui@intel.com>

	* doc/c-i386.texi: Document enqcmd.
	* testsuite/gas/i386/enqcmd-intel.d: New file.
	* testsuite/gas/i386/enqcmd-inval.l: Likewise.
	* testsuite/gas/i386/enqcmd-inval.s: Likewise.
	* testsuite/gas/i386/enqcmd.d: Likewise.
	* testsuite/gas/i386/enqcmd.s: Likewise.
	* testsuite/gas/i386/x86-64-enqcmd-intel.d: Likewise.
	* testsuite/gas/i386/x86-64-enqcmd-inval.l: Likewise.
	* testsuite/gas/i386/x86-64-enqcmd-inval.s: Likewise.
	* testsuite/gas/i386/x86-64-enqcmd.d: Likewise.
	* testsuite/gas/i386/x86-64-enqcmd.s: Likewise.
	* testsuite/gas/i386/i386.exp: Run enqcmd-intel, enqcmd-inval,
	enqcmd, x86-64-enqcmd-intel, x86-64-enqcmd-inval,
	and x86-64-enqcmd.

opcodes/ChangeLog:

2019-06-04  Xuepeng Guo  <xuepeng.guo@intel.com>
	    Lili Cui  <lili.cui@intel.com>

	* i386-dis.c (enum): Add MOD_0F38F8_PREFIX_1 and
	MOD_0F38F8_PREFIX_3.
	(prefix_table): New instructions (see prefix above).
	(mod_table): New instructions (see prefix above).
	* i386-gen.c (cpu_flag_init): Add entries for enqcmd.
	(cpu_flags): Add a bitfield for enqmcd.
	* i386-init.h: Regenerated.
	* i386-opc.h (enum): Add CpuENQCMD.
	(i386_cpu_flags): Add a bitfield for cpuenqcmd.
	* i386-opc.tbl: Add enqcmd and enqcmds instructions.
	* i386-init.h: Regenerated.
	* i386-tbl.h: Regenerated.