nir: Get rid of the array elements parameter on load/store intrinsics

nir: Get rid of the array elements parameter on load/store intrinsics

Previously, we used intrinsic->const_index[1] to represent "the number of
array elements to load" for load/store intrinsics.  However, this set to 1
by every pass that ever creates a load/store intrinsic.  Also, while it
might make some sense for registers, it makes no sense whatsoever in SSA.
On top of that, the i965 backend was the only backend to ever support it;
freedreno and vc4 just assert that it's always 1.  Let's just delete it.

Signed-off-by: Jason Ekstrand <jason.ekstrand@intel.com>
Reviewed-by: Connor Abbott <cwabbott0@gmail.com>
Reviewed-by: Rob Clark <robclark@freedesktop.org>