mips.md (SHORT): Fix long line.

gcc/
	* config/mips/mips.md (SHORT): Fix long line.
	(SUBDI): New mode iterator.  Extend the shift-and-truncate insns
	to QImode and HImoe.

gcc/testsuite/
	* gcc.target/mips/truncate-1.c: New test.

From-SVN: r128525