cris.md: Post-reload, split/generate clobberless memory destination moves

cris.md: Post-reload, split/generate clobberless memory destination moves

In preparation for compare-elimination (for it to be obviously
useful), we have to have some common insn in-between that
doesn't clobber condition-codes.  A move to memory is an obvious
choice.  Note the FIXME: we can do this for a zero source too;
later.

gcc:
	* config/cris/cris.md ("movsi"): For memory destination
	post-reload, generate clobberless variant.
	("*mov_tomem<mode>_split"): New split.
	("*mov_tomem<mode>"): New insn.
	("enabled", mov_tomem_enabled): Define and use to exclude "x" ->
	"Q>m" for less-than-SImode.