Add future.md.

2019-08-02  Michael Meissner  <meissner@linux.ibm.com>

	* config/rs6000/future.md: New file.
	* config/rs6000/rs6000.md: Include future.md.
	* config/rs6000/t-rs6000 (MD_INCLUDES): Add future.md.

From-SVN: r274030