X86: Decode opcode 0x82 as opcode 0x80 in 32-bit mode

Update x86 disassembler to treat opcode 0x82 as an aliase of opcode 0x80
in 32-bit mode.

gas/

	PR binutils/20754
	* testsuite/gas/i386/opcode.s: Add tests for opcode 0x82.
	* testsuite/gas/i386/opcode-intel.d: Updated.
	* testsuite/gas/i386/opcode.d: Likewise.

opcodes/

	PR binutils/20754
	* i386-dis.c (REG_82): New.
	(X86_64_82_REG_0): Likewise.
	(X86_64_82_REG_1): Likewise.
	(X86_64_82_REG_2): Likewise.
	(X86_64_82_REG_3): Likewise.
	(X86_64_82_REG_4): Likewise.
	(X86_64_82_REG_5): Likewise.
	(X86_64_82_REG_6): Likewise.
	(X86_64_82_REG_7): Likewise.
	(dis386): Use REG_82.
	(reg_table): Add REG_82.
	(x86_64_table): Add X86_64_82_REG_0, X86_64_82_REG_1,
	X86_64_82_REG_2, X86_64_82_REG_3, X86_64_82_REG_4,
	X86_64_82_REG_5, X86_64_82_REG_6 and X86_64_82_REG_7.