[OpenCL] Align vload and vstore builtins

Various vload and vstore builtins were missing or misdefined in the
TableGen description.  Align the OpenCL vload* and vstore* builtins of
the `-fdeclare-opencl-builtins` option to those of `opencl-c.h`.

Reviewed-by: Stuart Brady <stuart.brady@arm.com>