arm: MVE Don't use lsll for 32-bit shifts scalar

arm: MVE Don't use lsll for 32-bit shifts scalar

After fixing the v[id]wdups using the "moving the wrap parameter" into the
top-end of a DImode operand using a shift, I noticed we were using lsll for
32-bit shifts in scalars, where we don't need to, as we can simply do a move,
  which is much better if we don't need to use the bottom part.

We can solve this in a better way, but for now this will do.

gcc/ChangeLog:
2020-04-07  Andre Vieira  <andre.simoesdiasvieira@arm.com>

	* config/arm/arm.d (ashldi3): Don't use lsll for constant 32-bit shifts.