Add support for Intel CET instructions

Add support for Intel CET instructions

Support Intel Control-flow Enforcement Technology (CET) instructions:

https://software.intel.com/sites/default/files/managed/4d/2a/control-flow-enforcement-technology-preview.pdf

gas/

	* config/tc-i386.c (cpu_arch): Add .cet.
	* doc/c-i386.texi: Document cet.
	* testsuite/gas/i386/cet-intel.d: New file.
	* testsuite/gas/i386/cet.d: Likewise.
	* testsuite/gas/i386/cet.s: Likewise.
	* testsuite/gas/i386/x86-64-cet-intel.d: Likewise.
	* testsuite/gas/i386/x86-64-cet.d: Likewise.
	* testsuite/gas/i386/x86-64-cet.s: Likewise.
	* testsuite/gas/i386/i386.exp: Run Intel CET tests.

opcodes/

	* i386-dis.c (REG_0F1E_MOD_3): New enum.
	(MOD_0F1E_PREFIX_1): Likewise.
	(MOD_0F38F5_PREFIX_2): Likewise.
	(MOD_0F38F6_PREFIX_0): Likewise.
	(RM_0F1E_MOD_3_REG_7): Likewise.
	(PREFIX_MOD_0_0F01_REG_5): Likewise.
	(PREFIX_MOD_3_0F01_REG_5_RM_1): Likewise.
	(PREFIX_MOD_3_0F01_REG_5_RM_2): Likewise.
	(PREFIX_0F1E): Likewise.
	(PREFIX_MOD_0_0FAE_REG_5): Likewise.
	(PREFIX_0F38F5): Likewise.
	(dis386_twobyte): Use PREFIX_0F1E.
	(reg_table): Add REG_0F1E_MOD_3.
	(prefix_table): Add PREFIX_MOD_0_0F01_REG_5,
	PREFIX_MOD_3_0F01_REG_5_RM_1, PREFIX_MOD_3_0F01_REG_5_RM_2,
	PREFIX_0F1E, PREFIX_MOD_0_0FAE_REG_5 and PREFIX_0F38F5.  Update
	PREFIX_0FAE_REG_6 and PREFIX_0F38F6.
	(three_byte_table): Use PREFIX_0F38F5.
	(mod_table): Use PREFIX_MOD_0_0F01_REG_5, PREFIX_MOD_0_0FAE_REG_5.
	Add MOD_0F1E_PREFIX_1, MOD_0F38F5_PREFIX_2, MOD_0F38F6_PREFIX_0.
	(rm_table): Add MOD_0F38F5_PREFIX_2, MOD_0F38F6_PREFIX_0,
	RM_0F1E_MOD_3_REG_7.  Use PREFIX_MOD_3_0F01_REG_5_RM_1 and
	PREFIX_MOD_3_0F01_REG_5_RM_2.
	* i386-gen.c (cpu_flag_init): Add CPU_CET_FLAGS.
	(cpu_flags): Add CpuCET.
	* i386-opc.h (CpuCET): New enum.
	(CpuUnused): Commented out.
	(i386_cpu_flags): Add cpucet.
	* i386-opc.tbl: Add Intel CET instructions.
	* i386-init.h: Regenerated.
	* i386-tbl.h: Likewise.