*extendsi_truncate<mode>): Emit exts if supported.  Add attribute
	defintions.
	(*extendhi_truncateqi): New define_insn_and_sptit.

testsuite/
	* gcc.target/mips/octeon-exts-6.c: New test.
	* gcc.target/mips/extend-1.c: New test.
	* gcc.target/mips/octeon-exts-2.c: Adjust to not match sign-extension
	EXTS.
	* gcc.target/mips/octeon-exts-5.c: Likewise.

From-SVN: r147751