x86: Rename match_reg_size to match_operand_size

x86: Rename match_reg_size to match_operand_size

match_reg_size checks size for both memory and register operands.  This
patch renamed match_reg_size to match_operand_size and updated comments
for

commit 3ac21baa8498d3aa9951f79e2c3336d532eeff7b
Author: Jan Beulich <jbeulich@novell.com>
Date:   Mon Jul 16 08:19:21 2018 +0200

    x86: fix operand size checking

which added one argument to match_reg_size, match_simd_size and
match_mem_size.

	* config/tc-i386.c (match_reg_size): Renamed to ...
	(match_operand_size): This.  Update comments.
	(match_simd_size): Update comments.  Replace match_reg_size
	with match_operand_size.
	(match_mem_size): Likewise.
	(operand_size_match): Replace match_reg_size with
	match_operand_size.