[GlobalISel] Check if ShiftAmt is greater then size of operand

matchCombineShlOfExtend did not check if the size of new shift would be
wider then a size of operand. Current condition did not work if the value
being shifted was zero. Updated to support vector splat.

Patch by: Acim Maravic

Differential Revision: https://reviews.llvm.org/D151122