md.texi (Standard Names): Change insn pattern name from truncM2 to btruncM2 for 'trunc' built-in description.

	* doc/md.texi (Standard Names): Change insn pattern name
	from truncM2 to btruncM2 for 'trunc' built-in description.
	Add rintM2 insn pattern description.

From-SVN: r101159