S/390: movdf improvements

S/390: movdf improvements

This patch add the vector load element from immediate instruction to the
movdf/dd pattern for loading a FP zero and it removes the vector
instructions from the mov<mode>_64 pattern. These were pointless in
there because z13 support implies DFP support so these instructions will
always be matched in the mov<mode>_64dfp pattern instead.

Regression tested on s390x

gcc/ChangeLog:

2017-03-24  Andreas Krebbel  <krebbel@linux.vnet.ibm.com>

	* config/s390/s390.md ("mov<mode>_64dfp" DD_DF): Use vleig for loading a
	FP zero.
	("*mov<mode>_64" DD_DF): Remove the vector instructions. These
	will anyway by matched by mov<mode>_64dfp.

From-SVN: r246448