Change VLD3/4 and VST3/4 for quad registers to not update the address register.

These operations are expanded to pairs of loads or stores, and the first one
uses the address register update to produce the address for the second one.
So far, the second load/store has also updated the address register, just
for convenience, since that output has never been used.  In anticipation of
actually supporting post-increment updates for these operations, this changes
the non-updating operations to use a non-updating load/store for the second
instruction.

llvm-svn: 125013